Display unit and methods of displaying an image

ABSTRACT

The present invention provides a method of displaying an image on a display device having first and second sides, said image including an light restricting silhouette pattern having a plurality of first transparent or translucent areas, and at least one design layer having at least one color, said at least one design layer being visible from one side of said display device and substantially less visible from the other side, said image being substantially transparent or translucent as viewed from the other side, comprising the steps:  
     1) providing at least a definition of said design layer to a computer;  
     2) generating a computerized version of said design layer with the computer;  
     3) outputting the computerized version of said design layer to said display device, the computerized version of said design layer being modified to subdivide said design layer into a plurality of second discrete transparent or translucent areas and other areas, and  
     4) displaying said modified design layer and said silhouette pattern with said first and second transparent areas being in registry.  
     Articles produced in accordance with the method are also described.  
     Printers, raster image processing methods and systems, computer graphics systems are described for producing the article.

FIELD OF THE INVENTION

[0001] The present invention relates to a display unit, and inparticular to a display unit for displaying images viewable from twosides, whereby the image as perceived from one side can be differentfrom the image perceived from the other side and the display unit istransparent or translucent when viewed from one of the sides.

[0002] The invention also relates to a method of displaying such animage as well as printers suitable for displaying a printed image andraster image processing (RIP) systems for preparing the data beforedisplay, particularly before printing.

BACKGROUND OF THE INVENTION

[0003] Display devices with differing images on each side and beingtransparent or translucent from one of the sides are known from avariety of documents including EP-A-0170472 which describes a panelcomprising a light permeable material and a silhouette pattern,comprising any arrangement of light restricting material whichsubdivides the panel into a plurality of discrete light restrictingareas and/or a plurality of discrete transparent or translucent areas,characterized in that a design is superimposed on or forms part of saidsilhouette pattern so that said design is visible from one side of thepanel only, and wherein said design is less perceptible from said oneside of the panel as the level of illumination transmitted through thepanel from said other side increases. A number of different visioneffects are obtainable from different panels falling within the abovedefinition. Thus clarity of vision can be maintained from the one sideto the other side with the exception of the area covered by the designwith clarity of vision through the whole of the panel from the otherside to the one side. Visibility from the one side to the other side canbe totally or partially obstructed while there is clarity of visionthrough the whole of the panel from the other side to the one side, inother words a unidirectional vision effect is obtained Clarity of visionis obtainable from the one side to the other side except in the area ofthe design while visibility from the other side to the one side istotally or partially obstructed. Vision from either side can be totallyor partially obstructed. In all cases through vision can be obtained ineither direction through the panel when the level of illuminationperceived through the panel from the far side of the panel sufficientlyexceeds the illumination reflected from the near side of the panel. Thetransparent areas typically have dimensions ranging from 0.5 to 3 mm.

[0004] EP-A-0170472 and EP-00118638 describe methods of producing boththe silhouette pattern and also the imposed design. The methods asdescribed may be summarized as either sequential printing of thesilhouette and/or the design using screen lithographic or similar inkprinting processes with as exact a registration as can be obtained or amethod in which a mask is applied and the printing processes are carriedout through the mask onto the substrate. When the mask is removed, thesilhouette pattern and image remain on the substrate only in the areaswhich the mask or stencil allow the ink to penetrate.

[0005] EP-A-0234121 describes further methods of printing such an image.The printing methods are limited to those including inks. Again a maskis described which is subsequently removed taking with it unwantedportions of the silhouette pattern and image.

[0006] U.S. Pat. No. 5,396,559 describes a security device for use onidentification cards, monetary documents, and the like using a referencepattern and a message pattern each having the appearance of a randompattern of dots. The reference pattern is a dense pattern of randomlypositioned dots, and the message pattern is a modulated version of thereference pattern in which the dots of the reference pattern areslightly repositioned by an amount depending on the gray value or colorvalue of a message image at each dot location. The message image isdecrypted and becomes visible with a range of gray values when it isviewed through a film transparency of the reference pattern. The dotpattern may be printed, embossed or recorded as a photograph or ahologram. Decryption of the message image may be accomplished by viewingthrough a contact mask, superposition of images of the message patternand reference pattern, by viewing the message pattern through a maskpositioned at a real image of the reference pattern, or like means.

[0007] Japanese patent application Kokai 1 (1993)-57863 describes aproduction of an image including transparent sections for areas of theimage. A method is described in which a decorative sheet is prepared byregistration printing in the order of a rear pattern layer, a coveringink layer and a front pattern layer on a transparent plastic sheet insuch manner that a plurality of small transparent portions remain in theimage. No description is made as to how the registration printing shouldbe carried out.

[0008] Japanese patent application Kokai I(1989)-69397 describes amethod of producing a transparent plastic or glass substrate with aprinted layer including a plurality of holes. The method includesprinting the image onto a second substrate, perforating the image andsecond substrate and then transferring the image only from the secondsubstrate to the transparent plastic or glass substrate.

SUMMARY OF THE INVENTION

[0009] The present invention provides a method of displaying an image ona display device having first and second sides, said image including alight restricting silhouette pattern having a plurality of firsttransparent or translucent areas, and at least one design layer havingat least one colour, said at least one design layer being visible fromone side of said display device and substantially less visible from theother side, said image being substantially transparent or translucent asviewed from the other side, comprising the steps:

[0010] 1) providing at least a definition of said design layer to acomputer;

[0011] 2) generating a computerized version of said design layer withthe computer;

[0012] 3) outputting the computerized version of said design layer tosaid display device, the computerized version of said design layer beingmodified to subdivide said design layer into a plurality of seconddiscrete transparent or translucent areas and other areas, and

[0013] 4) displaying said modified design layer and said silhouettepattern with said first and second transparent areas being in registry.

[0014] The present invention also includes an article having aconformable substrate, comprising: a colorant receptor layer and a lightrestricting layer on said substrate, said light restricting layer havinga plurality of first transparent or translucent areas.

[0015] The present invention also includes an article comprising: apolymeric substrate having a composition comprising vinyl chlorideresin, optional acrylic resin, optional plasticizer, and optionalstabilizer, wherein the composition is formed on a polymeric releaseliner having smoothness of a Sheffield value of from about 1 to about10, and a light restricting layer and a design layer on said substrate,said design layer including at least one color layer, said lightrestricting layer being subdivided into a plurality of first transparentor translucent areas, said design layer being subdivided into aplurality of second transparent or translucent areas, and said first andsecond transparent areas being in registry.

[0016] The present invention further includes a printer for receiving aprint file including color separated image data, light restricting layerdata and transparency data, and for printing the color separated imageand the light restricting layer data including transparent areas in boththe color-separated layer and the light restricting layer in accordancewith the transparency data.

[0017] The invention further includes a raster image processing methodfor raster image processing of a print file including color separatedimage data, light restricting layer data and transparency data,comprising: operating on said print file to generate raster imagebitmaps for said color separated image data and said light restrictinglayer data, and introducing said transparency data into said rasterimage bitmaps for said color separated image data and said lightrestricting layer data so that the transparent areas in said colorseparated image raster bitmap and said light restricting layer bitmapare in registry.

[0018] The invention includes in addition a raster image processingsystem for raster image processing of a print file including colorseparated image data, light restricting layer data and transparencydata, comprising: means operating on said print file to generate rasterimage bitmaps for said color separated image data and said lightrestricting layer data, and means introducing said transparency datainto said raster image bitmaps for said color separated image data andsaid light restricting layer data so that the transparent areas in saidcolor separated image raster bitmap and said light restricting layerbitmap are in registry.

[0019] The invention also includes a graphics computer based system forcreating graphics images including color separated layers and lightrestricting layers, comprising: first input means for image data, meansfor generating color separated image data from said image data, meansfor generating light restricting layer data, second input means fortransparency data, and means for outputting a display file includingsaid color separated image data, said light restricting layer data andsaid transparency data.

[0020] The present invention may provide conformable articles includingtransparent areas in images, methods of providing the same and printers,computer graphics systems and raster image processing systems andmethods for producing images on the articles at low cost.

[0021] The present invention may provide conformable articles includingtransparent areas in images, methods of providing the same and printers,computer graphics systems and raster image processing systems andmethods for producing images on the articles which allow variability inimage not previously achieved. The invention with its embodiments andadvantages will be described with reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 shows a schematic cross section of a display unit inaccordance with the present invention;

[0023]FIG. 2 shows a block diagram of a display system in accordancewith the present invention.

[0024]FIG. 3 a complex image including transparent areas in accordancewith the present invention.

[0025]FIGS. 4A and B show characters and shapes defined by transparentareas in accordance with the present invention.

[0026]FIG. 5 the graying effect of conventional light colored windowgraphics as seen in the prior art.

[0027]FIG. 6 shows a schematic cross-section view of a second embodimentof a display unit in accordance with the present invention.

[0028]FIG. 7 shows a cross-section view backlight for use with thesecond embodiment of the present invention.

[0029]FIG. 8 shows a schematic cross-section view of a third embodimentof a display unit in accordance with the present invention.

[0030]FIG. 9 is a cross-section through a printed substrate inaccordance with the present invention.

[0031]FIG. 10 is a cross-section through another printed substrate inaccordance with the present invention.

[0032]FIG. 11 is a cross-section view of a printing substrate inaccordance with a seventh embodiment of the present invention.

[0033]FIG. 12 is a cross-sectional view of a of a printing substrate inaccordance with an eighth embodiment of present invention.

[0034]FIG. 13 is a cross-sectional view of a printing substrate of atenth embodiment of the present invention.

[0035]FIG. 14 illustrates a cross-sectional view of a durable, opticallyclear, transparent layer of the eleventh embodiment of the presentinvention prepared on a polymeric release layer.

[0036]FIG. 15 illustrates a cross-sectional view of the durable,optically clear, transparent layer of the eleventh embodiment during alamination step.

[0037]FIG. 16 illustrates a cross-sectional view of the durable,optically clear, transparent layer of the eleventh embodiment incombination with an imaged substrate.

[0038]FIG. 17 illustrates a cross-sectional view of the durable,optically clear, transparent layer of the present invention incombination with an imaged substrate as a modification as a twelfthembodiment of the invention.

[0039]FIG. 18 is a block diagram of the components of a printing systemin accordance with embodiments fourteen to sixteen of the presentinvention.

[0040]FIG. 19A is a cross-section and 19B is a top view of a printedsubstrate for use with embodiments fourteen to sixteen of the presentinvention.

[0041]FIG. 20 is a schematic drawing of a printing head in accordancewith the fifteenth embodiment of the present invention.

[0042]FIG. 21 is a schmatic drawing of a printer in accordance withanother embodiment of the present invention.

DEFINITIONS

[0043] As used in this application:

[0044] “colorant” means any material that imparts color to anothermaterial or mixture and maybe either, dyes or pigments;

[0045] “colorant receptor layer” means any layer on a printing substratewhich is provided for the purpose of transferring colorants to thesubstrate.

[0046] “durable” means the substrates used in the present invention arecapable of withstanding the wear and tear associated with signage andmay be 2 to 5 years in exterior environments;

[0047] “plastic” means a material that is capable of being shaped ormolded with or without application of heat and include thermoplasticstypes, thermosets types, both of which may be flexible, semi-rigid orrigid, brittle or ductile;

[0048] “smear-resistant” as used in this application means resistant ofthe ink jet ink to smear as described in the following test, printing animage with black lines, allowing a minimum of five minutes time to dry,rubbing the line with the pad of the finger with a light to moderatepressure, such as might be used during normal handling of images, andobserving whether spread of the line occurs;

[0049] “durable” means the substrates useful in the present inventionare capable of withstanding the wear and tear associated with signageand may be used 2 to 5 years in exterior environments;

[0050] “conformable” means the substrates in a direct print film arecapable of conforming to uneven surfaces and retaining such conformationduring use without significant force applied per unit area of the film.Typically the conformable substrate can be adhered with hand pressureand conform to a surface having periodic or compound irregularities,such as a rivet or welded ridge on the exterior metallic surface of atractor trailer, without the substrate lifting from the surface.Preferably, a conformable substrate in a direct print film exhibits ayield point and/or permanent strain when subjected to a maximum tensilestress of about 3.5×10⁷ N/m² (5000 lb./square inch) at room temperatureaccording to ASTM D638-94b (1994), when the caliper used for the testincludes the total cross-sectional thickness of the substrate, thethickness of the adhesive, and the thicknesses of any further layerssuch as ink receptor, conductive or dielectric layers. More preferably,the maximum tensile stress limit is about 1.4×10⁷ N/m² to provide moreconformable films. Most preferably, the maximum tensile stress limit isabout 7×10⁶ N/m² to provide even more conformable films. Conformabilityof the films still require internal integrity. Desirably, the minimumtensile stress limit is about 6.9×10⁴ N/m² (10 lb./square inch) andpreferably the minimum tensile stress limit is about 1.7×105 N/m² (25lb./square inch).

[0051] Testing Methods

[0052] Bulk Powder Resistivity: “The Application of ZELEC ECP in StaticDissipative Systems” (Du Pont Chemicals, Deepwater, N.J. September 1992)

[0053] Specific Resistance: “Tego Conduct S Resistivity Measurement andApparatus” (available from Esprit Chemical Company, Rockland, Md.)Surface Resistance: ASTM D 4496-87 and ASTM D 257-93 published byAmerican Society for Testing and Materials.

[0054] Color Shift: ASTM D 2244-93 published by American Society forTesting and Materials.

[0055] Color Density: “Reflective Optical Density on a Status T Method””under the requirements of ANSI/ISO 5/3-1984, ANSI PH2. 18-1985 publishedby the Graphic Communications Association of Arlington, Va. Reflectedoptical density is measured using techniques well known to those in theprinting industry. Examples herein were evaluated with a Gretag SPM50densitometer from Gretag Limited, CH-8105 Regensdorf, Switzerland. Otherinstruments will give similar comparisons, but not necessarily the samevalues. “Color Density” is the measure of the intensity of theindividual primary colors on a recording medium to form the latent imageand is important to films of the present invention because color densityhas a major impact upon the perceived aesthetics of the image on therecording medium. By comparison, transmission optical density may bemeasured using an optical densitometer such as a Macbeth TD 904.

[0056] Sheffield: Sheflield method measurement described in TAPPI Test T538 om-88 published by the Technical Association of the Pulp and PaperIndustry of Atlanta, Ga.

[0057] The disclosures of the Testing Methods are incorporated herein byreference.

[0058] Embodiments of the Invention

[0059] The figures are intended for illustrative purposes only. Certaindimensions may have been exaggerated to improve clarity.

[0060]FIG. 1 shows a schematic cross section through a display unit ofthe kind used with the present invention. A display includes a firstsilhouette pattern 2, comprising an arrangement of light restrictingmaterial which subdivides the panel into a plurality of discrete lightrestricting areas 5 and/or a plurality of discrete transparent ortranslucent areas 6. The light restricting areas 5 have lighttransmission reducing properties. These may be, in one extreme,completely opaque, i.e. the optical density in transmission is infinite.Transmission optical density TOD (which is to be distinguished fromreflection optical density, ROD) is defined by the formula:${{TOD} = {\log_{10}\left( \frac{I_{i}}{I_{t}} \right)}},$

[0061] where I_(i) is the intensity of the incident light on the samplematerial and I_(t) is the intensity of the transmitted light passingthrough the material. The present invention accepts that the lightrestricting layer 5 may not be perfectly opaque but may allow some lightto transmit. It is preferred if the TOD of the light restricting layeris greater than 1, preferably greater than 2, more preferably greaterthan 2.5 and most preferably 3 or greater.

[0062] The translucent or transparent areas 6 allow light to passthrough. In one extreme the transparent areas 6 transmit all light andreflect or scatter no light, i.e. a TOD of infinity and a ROD ofinfinity, where the optical density in reflection is given by:${{ROD} = {\log_{10}\left( \frac{I_{1}}{I_{R}} \right)}},$

[0063] I_(R) being the reflected light intensity.

[0064] The present invention accepts that the translucent/transparentareas 6 may not be perfect light transmitters, i.e. they may absorband/or reflect and/or scatter some light. It is preferred if the TOD ofthe transparent or translucent areas have an ROD of less than 1,preferably less than 0.5. The translucent areas 6 should differ inoptical density from the light restricting areas 5 by a sufficientamount to make a clear visual difference. The TOD difference betweenareas 5 and 6 should preferably be greater than 0.3. According to thepresent invention the areas 6 are preferably transparent, morepreferably optically clear.

[0065] The pattern of light restricting 5 and/or transparent/translucentareas 6 may be any array of pixels, for example, a pattern of parallellines, dots, circles, squares, etc. which may be arranged in a regulararray, in the form of a design, in an irregular array or in a randomway. The transparent areas 6 may have any dimension depending upon thedisplay device used, and may be diameters typically in the range of 0.1mm to 8 mm, preferably 0.2 mm to 3 mm. The ratio of the transparentareas 6 to light restricting areas 5 may be chosen as desired but istypically 0.3 to 3, usually about 1, i.e. 50% Of the surface area iscovered by transparent areas 6. In accordance with the present inventionthe silhouette pattern 2 may be provided by any spatial light modulatoror filter which comprises a plurality of discrete light restrictingareas 5 and/or a plurality of discrete transparent or translucent areas6. The spatial light modulator or filter 2 may be a silhouette patternsimilar to that described in EP-A-0170472 or a pattern created by theback-light of a liquid crystal (LCD) display device or any otherappropriate display device.

[0066] Substantially coextensive with the spatial light modulator orfilter 2 is placed a display device 3 and/or a display device 4. Displaydevice 3 or 4 can display an image which may be a full color imagerepresented schematically by the four layers 7-10, 7′-10′ and the imageis divided into transparent or translucent areas 6 and colored designareas 7-10,7′-10′ so that the transparent or translucent areas 6 of thespatial light modulator or filter 2 are aligned (in registry) with thetranslucent or transparent areas 6 of display device 3, 4. The displaydevice 3 or 4 may be a printed image, for instance, in accordance withEP-A-0170472 or similar, or may be a LCD or LED display device which iscapable of displaying a monochrome or full color image. At least one ofdisplay device 3 or 4 may be a black or dark colored pattern.

[0067] The display unit 1 may be self-standing or may be laminated to asubstrate such as a transparent sheet of glass-like or polymericmaterial. The glass or polymeric sheet may be laminated to the displaydevice 3, the display device 4 or may be interposed between any of thelayers 7-10,7′-10′ or between display device 3 and silhouette pattern 2or between silhouette pattern 2 and display device 4. The substrate maybe the window of a car, bus or building or may be a flexible polymericsheet. When the display device 3 or 4 is black or a dark color and islocated next to the transparent sheet 1, the dark display device 3, 4may be partly or completely provided by tinting the transparent sheet astaught in EP Patent No. 0 133 761.

[0068]FIG. 2 shows a schematic block diagram of the first embodiment ofthe present invention. A suitable graphics image for display purposes isgenerated in image generation means 12. The image may be generated usingcomputer 13 and special software developed for production of graphicimages such as Adobe Photoshop™, Adobe Illustrator™, Corel-Draw™, Aldus®Pagemaker™, Quark Xpress™ or similar. The image generation means 12 maybe a scanner with which all or part of picture information from animage, a picture or photograph is converted point by point intoelectrical signals to be stored in computer 13 as digital data.

[0069] Once the graphics image has been stored in computer 13 as amatrix of digital data which include sufficient data to determine theluminosity and color of each pixel of information, the data may beprepared such that it may be displayed with a plurality of transparentareas 6 within the graphics image.

[0070] In accordance with the present invention this may be done inseveral different ways:

[0071] Method 1. The color-separated layers of data (conventionallyCMYK, cyan, magenta, yellow and black or if the black layer is not used:CMY) may be modified to include no color data representing thetransparent areas 6 in each of the layers. This modification to the datamay be done in computer 13 but the invention is not limited thereto. Thepattern of transparent areas 6 may be provided by overlaying thetransparent areas 6 as areas of “no-color” onto the graphics imagewithin computer 13. The no-color data may be stored as raster or pixeldata. In general there is no need to modify the half-tone algorithms asdisclosed for instance in U.S. Pat. Nos. 5,253,084; 5,258,832;5,264,926; or 4,758,886 used to create the full color image. However, ifsmall diameters of the transparent areas are used (<0 5 mm) it may beadvisable to select the size of the transparent areas 6 and theirspacing so that they are not a multiple of the size of halftone cells inorder to avoid rhythmic color shifts. With small size transparent areas6, method 2 is preferred. The translucent/transparent areas 6 may be aregular, irregular, or random array of dots, lines, squares, circles,polygons, or similar, or a separate array of these representing a designor image. Both the size and the distribution of the transparent areas 6may be varied through the image.

[0072] As shown in FIG. 3 the transparent areas 6 may be a complex andattractive design 5, 6, 11 which has image portions 22 which may belight restricting and a transparent design portion 23 made up oftransparent/translucent areas 6 surrounded by image areas which may belight restricting areas 5. The transparent areas 6 may have differingdiameters and shapes in order to represent the detail of the designcorrectly. It is understood that on the reverse face of the design 22,23, a fill color image 3 or 4 may be displayed. The representation ofthe filigree patterns of the fern leaves in a plurality of transparentareas 6 which are in registry through multiple layers of printingrequires exact printing of small size repetitive transparent areas 6separated by substantially opaque regions 5 in order to create a vividand clear design.

[0073] Method 2. The data representing the transparent areas is storedin a separate layer—a “T” layer—in computer 13. A display output filefrom computer 13 includes the color separated primary printing colorlayers, CMYK or CMY layers, plus the T layer. As will be describedlater, the information in the T layer may be used in different ways Forinstance, where Raster Image Processing (RIP) is carried out, the dataof the T layer may be introduced into each of the CMYK layers in thefinal raster bitmap during or immediately after the RIP. Introducingthis data into the raster bitmap has the advantages that smallrepetitive structure distortion may be reduced and the registration ofthe final image may be improved, as each color separated bitmap has theidentical positions of the transparent areas. Alternatively the T layermay bypass the RIP and be used by a display control circuit to controlthe display 3,4 in such a way that the transparent areas 6 aregenerated. For instance, where the display device 3,4 is a printer, thetransparent areas 6 may be generated by activating or deactivating theprinter head during printing in accordance with the T layer data.

[0074] Method 3. Method 3 is a modification of method 2 and uses aseparate transparent data layer T. The difference lies in the form ofthe data. In accordance with method 3, transparency data is stored inthe same way as dot matrices are stored, except instead of a dotrepresenting a colored dot in the final display the dot represents atransparent area 6. All the techniques of word processing and graphicssoftware can be duplicated in the inverse: instead of colored dots on awhite background, the data represents a transparent areas in a lightrestricting background. For instance, the data may be stored astransparent fonts. Thus a letter such as “I” is stored in the computeras a character which includes a predetermined array of transparent areas6 as shown schematically in FIG. 4A. When in the “T” mode, i.e. whengenerating the data for the transparency layer T, the key stroke “I”stores the array of transparent areas 6 shown in FIG. 4A. Similarlytransparency graphic programs can be used to create designs intransparent areas. Thus straight lines or shapes may be generated.Graphic elements: a rectangle and a line of transparent dots, are shownschematically in FIG. 4B.

[0075] Method 4 is a modification to method 1 in which the silhouettelayer 2 is included in addition to the CMYK or CMY layers. Thesilhouette layer 2 may generally be included as a light colored spotcolor, in particular, white. It contains the transparency data inregistry with the transparency data in each of the CMY or K layers.

[0076] Method 5 is a modification of method 2 in which the silhouettelayer 2 is included in addition to the CMYK or CMY layers. Thesilhouette layer 2 may generally be included as a light colored spotcolor. In preparing the silhouette layer 2 for display, the same methods(e.g. RIP) may be used as described for the CMYK or CMY layers.

[0077] Method 6 is a modification of method 3 in which the silhouettelayer 2 is included in addition to the CMYK or CMY layers. Thesilhouette layer 2 may generally be included as a light colored spotcolor. In preparing the silhouette layer 2 for display, the same methods(e.g. RIP) may be used as described for the CMYK or CMY layers.

[0078] Method 7 is a modification to method 4 in which the image ofdisplay device 4 is included in addition to the first image of displaydevice 3 and the silhouette layer 2. The second image may generally beincluded as further CMYK or CMY layers. These contain the transparencydata in registry with the transparency data in all of the other layers.

[0079] Method 8 is a modification of method 4 in which the image ofdisplay device 4 is included in addition to the first image of displaydevice 3 and the silhouette layer 2. In preparing the second image 4 fordisplay, the same methods (e.g. RIP) may be used as described for theCMYK or CMY layers of the first image 3.

[0080] Method 9 is a modification of method 6 in which the image ofdisplay device 4 is included in addition to the first image of displaydevice 3 and the silhouette layer 2. In preparing the second image 4 fordisplay, the same methods (e.g. RIP) may be used as described for theCMYK or CMY layers of the first image 3.

[0081] For Methods 1-9, the image is output to a display device 14which, in accordance with the present invention, may be a direct displaydevice similar to an LCD or LED display, an indirect printing device16-19, or a direct printing device 20, 21.

[0082] The method of displaying the data depends upon the method ofstoring the data.

[0083] Methods 1, 2 and 7. As these methods have the transparency datastored in each of the layers of the CMYK or CMY data, the CMYK or CMYdata can be handled as in conventional display devices provided thesecan display the number of layers for the particular method.

[0084] Methods 2, 3 5, 8 and 9 include a separate “T” layer, which maybe processed by display devices according to the present invention. Onsome existing graphics software it may be possible to specify atransparent spot color or to specify a spot color of any desired colorbut modify the display device so that it displays this spot color astransparent. In accordance with this application, devices capable ofprocessing data according to methods 2,3,5,6,7,9 are called transparencylayer display devices or TLD devices.

[0085] When the display device 3 or 4 of FIG. 1 is viewed from the frontand the level of illumination on that side is high, the transparentareas 6 appear dark, normally black. If the image to be displayed issimply provided with transparent areas 6 without modification to thecolors of the image, this image appears uniformly darker than theoriginal. This is particularly noticeable when the display device 3,4 isplaced adjacent to the same image in which there are no transparentareas 6. This can occur when the display device 3,4 covers the window ofa vehicle and the graphics continue onto the body of the vehicle. Thisis shown in FIG. 5 (Prior Art) which a photocopy of a photograph of atrain in which large white lettering has been applied over the side ofthe train. The white lettering passes over windows which have beencovered with conventional punched film window graphics. The grayappearance of the window areas 54 in comparison to the adjacent areas 52on the body of the train can be clearly seen. Hue changes can also occurin the arrangement such described with respect to FIG. 3 in which fullcolor portions 22 of the image may be adjacent to portions 23 withtransparent areas 6.

[0086] The following embodiment of the present invention provides asolution to this problem.

[0087] The technique of undercolor removal is known in printing andphotography (see for example “The Reproduction of Color in Photography,Printing & Television”, Fountain Press, UK, Second Impression 1988).Instead of printing or displaying dark areas of the image with acombination of the three traditional colors Cyan, Magenta and Yellow,using undercolor removal the black component of the color is providedseparately, e.g. by using separate black toners or inks. In accordancewith the present embodiment of the invention this technique is used in anovel way. When preparing the data for display, the computer graphicsprogram of computer 13 of FIG. 2 carries out undercolor removal in thenormal way, however, the apparent dark color of the transparent areas 6is taken into account in the undercolor removal. For example, if 50% ofthe image area is provided by transparent areas 6, a color with a blackcomponent of 50+X % will be displayed with only a black component of X%. The color displayed is the true color as the remaining 50% black isprovided by the transparent areas 6 which appear black. For a color withless than 50% black, no black is displayed. This results in somedarkening of the color with respect to the original but the total effectis still improved. To prevent differences in hue between light coloredareas of the image with and without transparent areas 6, the lightcolored areas of the image which do not have the transparent areas 6(e.g. outside window areas or area 22 of FIG. 3) are provided withadditional black—in effect undercolor addition. With the example givenabove, if a color only has a 10% black component, this component isremoved as completely as possible from this color in the areas of thetransparent areas 6. In parts of the image without transparent areas 6,this same color has 40% black added so as to match the hues throughoutthe image.

[0088] It is accepted that with some of the embodiments of the presentinvention the display device 4 may be partly visible from the other sideof the silhouette layer 2, i.e. viewed from the side of display device3. This may be due to the fact that the silhouette layer 2 can not beproduced (e.g. by some kinds of printing methods) with such opacity thatthe display device 4 is totally isolated optically. When display device4 has a dark color, the result of a light restricting but not opaquesilhouette layer 2 is that all the colors of display device 3 becomedarker. In accordance with the present invention, any darkening of theimage displayed on display device 3 is also compensated for byundercolor correction, or if this is not possible, by increasing theblack content of any part of the image 3 which lies outside the areawhere there are transparent areas 6.

[0089] A further method of compensating for the darkening effect of thetransparent areas 6, is to partly metallize these areas. This has theeffect of reducing transmission but provides a gain in reflected whitelight from the image 3. To achieve metallization, the whole area of thesubstrate may be partly metallized using techniques known for two waymirrors.

[0090] A direct or simultaneous display device 15 in accordance with thepresent invention is a display device which displays at least the imagedirectly from the electrical output of the computer 13 and combines thiswith the silhouette pattern 2 so that the transparent areas 6 of thesilhouette layer 2 are in registry with the transparent areas of theimage. Such a direct display device 15 in accordance with a secondembodiment of tile present invention is shown schematically in FIG. 6. Aconventional LCD display 24 is addressed by an addressing unit 28 whichis connected to the computer 13 in the conventional way e.g. by means ofcable and connector 29. The LCD array 24 may form part of a window.Behind the LCD array 24 is placed a back-light or reflector 25 which hasa light source 26 connected to a suitable power supply (not shown) bycable and connector 27. The back-light 25 produces illumination in theform of strips, squares, circles or similar shapes separated by areas oftransparent material such as to produce the silhouette pattern 2 asshown in FIG. 1. An example of such a back-light 25 is shownschematically in FIG. 7. The back-light 25 consists of a series ofoptical fibers 30 producing distributed light separated by transparentareas 31 which may be a transparent material such as optically clearacrylic resin. The optical fibers 30 are modified so that theydistribute the light from the light source 26 and emit the light in adistributed way along their length in a direction perpendicular to theplane of the back-light 25 towards the LCD display 24. This may be doneby introducing an irregularity 32 called an optical element such as aslit, on the surface of each fiber 30 away remote from the LCD display24. Such optical fibers 30 including optical elements 32 for producing adistributed series of cones of light are described in the articleentitled “Control of light output from plastic optical fiber withoptical elements” by Mary Poppendieck and David Brown, published at theInternational Congress and Exposition of the Engineering Society forAdvancing Mobility Land Sea Air and Space, Feb. 26-29 1996.

[0091] When the optical elements 32 are arranged on the side of eachoptical fiber 30 which is remote from the LCD display 24 then theindividual cones of light are reflected towards the LCD display 24 suchas to illuminate parts, e.g. strips or rectangles of the LCD display 24.As explained in the above mentioned article, the spacing of opticalelements 32 along the fiber 30 may be arranged so that the spacing ofthe elements 32 is closer together or intrude deeper into the fiberdependent upon the distance from the light source 26. In this way, auniform extraction of light along the length of the fiber 30 may beachieved.

[0092] Further descriptions of how to produce a back light from opticalfibers are given in U.S. Pat. Nos. 5,226,105; 4,907,132; 4,885,663;4,845,596; 4,519,017; 4,234,907; 5,432,876, 5,187,765; and 5,005,931;all of which are incorporated herein by reference.

[0093] The LCD display 24 is driven by the computer 13 via cable andconnector 29 and addressing unit 28 so that only those liquid crystalcells of LCD display 24 which are illuminated by the optical fibers 30are addressed with data of the image 3 or 4 of FIG. 1 of the presentapplication prepared in accordance with method 2 or 3 above. When thetransparent areas are small, it is preferred if the introduction of thetransparent areas in the data is delayed until immediately beforedisplay. For instance, the output data file for the image on the displaydevice is first prepared in the computer 13. Then the transparent areas6 are introduced. It has been found that, particularly when thetransparent areas 6 are small and are in a regular array, introducingthe transparent areas at an earlier stage may result in distortion ofthese areas, when the image is manipulated by other algorithms, e.g.filters.

[0094] The under color removal mentioned above is carried out allowingfor the percentage of transparent areas 6 in the image 3,4 to bedisplayed. In the areas of the LCD display 24 which are opposite thetransparent areas 31 of back-light 25, the computer 13 outputs therelevant data so that the LCD display 24 is transparent in these areas.Thus the image 3,4 displayed on LCD display 24 consists of areas of theimage 3 or 4 illuminated by optical fibers 30 separated by transparentareas 31. When viewed from the front of the LCD display 24, a full image3 or 4 may be seen separated by the transparent areas 6 which appeardark when the general illumination on the back-side of the LCD display24 is lower than the general illumination on the front side of the LCDdisplay 24. On the other hand, when viewed from the back of the LCDdisplay 24, the display device 25 has transparent areas 31 separated byopaque areas provided by the back of the optical fibers 30.

[0095] In accordance with a modification of the second embodiment theback-light 25 may be provided by a series of LED units 33 separated bytransparent areas 34 as shown in FIG. 8 schematically. The LED elements33 may be formed in lines or squares or circles or in similar shapes andare arranged so that the light emitted from the LED elements 33 isprojected towards the LCD display 24. Thus the LED elements 33illuminate those parts of LCD display 24 which contain image data fed tothe LCD display 24 via connector and cable 29 and addressing unit 28from the computer 13. The data output from the computer 13 providestransparent areas in the LCD display 24 which are in registry with thetransparent areas 34 of the back-light 25 shown in FIG. 8.

[0096] Alternatively, the display device 14 in accordance with a thirdembodiment of the present invention may be an indirect printing device16-19.

[0097] An indirect printing device in accordance with the presentinvention is a printing method with which there is sequential coloranttransfer of individual color-separated images from intermediate imagecarriers to the printing substrate. Typically this requires a set ofcolor-separated, i.e. single primary color, intermediate imagesubstrates 17 which are used in printing device 18 to produce the finalprinted image 19. The intermediate imaged substrates 17 are producedfrom the computer output data in the intermediate imaging device 16.Such an indirect printing method may be for example lithographic orscreen printing.

[0098] With reference to lithographic printing, the imaged substrates 17may be a series of imaged polyester lithographic plates, suitable forlithographic printing on a printing press 18. The lithographicsubstrates 17 may be generated directly from the information from thecomputer 13 in a suitable imaging device 16. The set of lithographicsubstrates 17 may be used to print sequentially all or part of the image4, silhouette pattern 2 and image 3 of FIG. 1 in accordance with thepresent invention. For instance, as shown schematically in FIG. 9, theimage 4 may be a pattern of black 42 on a transparent sheet 41 inregistry with an light restricting white silhouette pattern 43 ontowhich is printed in registry a full 4-color image 44-47 leavingtransparent areas 48. Data preparation may be performed by any of themethods 7 to 9 above. Thus, a total of 6 plates 17 maybe necessary:black, white, cyan, magenta, yellow and black. An individual plate 17may be used several times for each color in order to obtain sufficientdepth of color or opacity of the printed layer 42-47. Where a darktinted transparent sheet 41 is used it may be possible to omit the firstblack layers and use only five color layers: white, cyan, magenta,yellow and optionally black. Data preparation may then be made inaccordance with any of the methods 4 to 6 above. In order to obtain goodregistration between the various lithographic substrates 17, they may beproduced by a method described in co-pending European patent applicationEP 95106746.1 filed on May 4, 1995 which is incorporated herein byreference.

[0099] After preparation of the intermediate imaged substrates 17 fromthe image data, the final prints 19 are produced in printers 18 in theconventional way on clear films. The printing films used for all theembodiments of the present invention involving printing are conformabledue to the conformable nature of the substrates selected and theconformable adhesive layer contacting one major surface of thesubstrate.

[0100] An alternate sequence of color layers 42-47 may be printed asshown schematically in FIG. 10. The order of the layers 42 to 47 isreversed and the last color printed is the black layer 42. As applied toa window substrate, transparent substrate 41 may now form the outerlayer or overlaminate of the sheeting 40. An adhesive layer 50 may beapplied optionally to the printed side of sheeting 40 in order to securethe sheeting 40 to a window or similar. Adhesive layer 50 may be any ofthe adhesives mentioned below with reference to overlaminates. It ispreferred if the transparent substrate 41 of FIGS. 9 and 10 is theoptically clear vinyl sheeting in accordance with the eleventhembodiment of the present invention. It is also preferred if theadhesive layer 50 is optically clear, preferably an acrylic pressuresensitive adhesive.

[0101] Although it is preferable to use a pressure-sensitive adhesive,any adhesive that is particularly suited to the particular substrateselected and end-use application can be used on the sheeting 41. Suchadhesives are those known in the art any may include adhesives that areaggressively tacky adhesives, pressure sensitive adhesives,repositionable and/or positionable adhesives, hot melt adhesives and thelike Pressure sensitive adhesives are generally described in Satas, Ed.,Handbook of Pressure Sensitive Adhesives 2nd Ed. (Von Nostrand Reinhold1989), the disclosure of which is incorporated by reference.

[0102] Also, as indicated in FIG. 10, any errors in registration betweenthe printed layers 42-47 may be compensated for by making thetransparent areas 48 in the silhouette pattern, i.e. the white layer 43,slightly smaller than in the colored layers 44 to 47. Similarly, thetransparent areas 48 in the black layer 42 may be made slightly smallerthan the areas 48 in the white layer 43. By this means, missregistrationof the colored layers will not encroach into the transparent area 48,similarly missregistration of the white layer 43 will also not encroachinto the transparent areas 48 of black layer 42.

[0103] The intermediate imaged substrates 17 may also be a set ofscreens for a screen printing device 18. The output from computer 13 isthen fed to an automatic screen producing device 16 as is known to askilled person in screen printing techniques. The final image 19 isproduced by sequential printing of the colors using the screens 17 andconventional screen printing techniques.

[0104] A major disadvantage with indirect printing methods is that theintermediate imaged substrates 17 are located in a printing device 18 insequence and the maintenance of exact registration between the variouslayers of images 3 and 4 and silhouette pattern 2 of FIG. 1 is difficultor requires time consuming proofing and adjustment. Some improvement maybe obtained by using a full color laser printer. In this case theintermediate imaged substrates 17 are provided by the imagedsemi-conductive drums used to print substrates 19 by means of theattraction of toner to the charged electrostatic areas of the drum.Providing six or more drums requires a special printer which isexpensive, or in the alternative, using the same drum six times may makeexact registration difficult. The AGFA Chromapress™ electrostaticprinting system supplied by AGFA-Gevaert NV, Mortsel, Belgium, may be anindirect printer in accordance with the present invention. The systemincludes 8 electrostatic printer drums arranged as a series of fourdrums on each side of the substrate to be printed. The printing drumsare controlled by a computer graphics system suitable for producing themodified images in accordance with the present invention. This system isdesigned for printing onto paper but could be modified to print ontoclear films, especially optically clear polyester films of the typeknown for overhead transparencies.

[0105] It is preferred in accordance with fourth to sixteenthembodiments of the method of the present invention if the display device14 is a direct printing device 20. In accordance with the presentinvention a direct printing device is capable of deposition of colorantsof a full color image directly to a single printing substrate. Theprinting substrate may be the final printed article or an intermediatesubstrate. Hence a direct printing method is one which does not make useof a set of intermediate imaged substrates 17 which must be used insequence in order to print a substrate 19 in a printer 18. A directprinting device 20 in accordance with the present invention is able toconvert the signals from the computer 13 into a full color, image on asubstrate 21 or a single intermediate substrate used for transferringthe image, e.g. a decal, in order to produce, for example, the sheeting40 shown schematically in FIG. 9 or 10.

[0106] Such direct printing methods may include but are not limited to,ink-jet including bubble jet and spark jet, thermal and piezoelectricimpulse jet, thermal transfer including sublimation or mass thermaltransfer or electrostatic or electrophotographic printing methods. Inaccordance with the present invention a direct printing method may alsobe the electrostatic transfer method known as ScotchPrint™ ElectronicGraphics System available from Minnesota Mining and ManufacturingCompany in which an electrostatic image is first created on specialelectrostatic paper and then is transferred in a single operation to atransparent substrate 21. The distinction between the ScotchPrint™process described above and the indirect printing methods such as screenprinting or lithographic printing is that the transfer of the image iscarried out with a single substrate and is in full color whereas theindirect printing methods make use of a set of color separated imagedsubstrates 17 in order to generate a full color image. The registrationof electrostatic printing may be considerably better than that of anindirect printer method, independent of whether the transfer process isused.

[0107] An example of a printing process used in the present inventioncomprises feeding the material 41 in either sheet form or dispensed froma roll into a printer, printing a desired color image and silhouettepattern 42-47 in accordance with the present invention, retrieving theimage from the printer and, optionally, overlaminating the image with afilm 50 to protect the receptor coatings and image from water,scratching and other potential sources of damage to the image, and thenremoving the release liner, and affixing the printed image to atransparent substrate for viewing.

[0108] It is preferred if the direct printing method has good localregistration. An example of good local registration printing is thatproduced by a conventional high quality ink-jet printer which printsrelatively local areas of full color. Thus, very high qualityregistration can be obtained locally on the receptor medium. As veryhigh definition is required around each small transparent area in theimage, good local registration may be advantageous and some distortionof the complete image over long distances may be tolerated. On the otherhand, electrostatic printers have distances of several centimetersbetween each color station so that full color printing is not carriedout as locally as ink jet printers, even with single pass machines.

[0109] Many factors may affect the local registration of printing. Inkjet printers move the substrate a distance of 2-3 mm between colors,whereas a single pass electrostatic printer moves the substrate between100 and 150 mm and a thermal transfer printer such as the SummagraphicsSummachrome™ Imaging system prints the whole area before changing color.Tests have indicated that the amount of movement between color changesis not a reliable guide to the degree of local registration.

[0110] Printers are often characterized by “dots per inch” or DPI. Testshave indicated that DPI is a better guide but not an infallible one forthe choice of printer in accordance with the present invention as can beseen from Table 1 below.

[0111] Warp or distortion or thermal expansion/contraction of thesubstrate 21 or of intermediate substrates 17 may also affect or reducethe theoretical level of local registration.

[0112] It has been determined that the degree of local registration canbe determined practically by printing a special test image whichincludes a special full color image with a regular array of transparentcircles of different diameters in the image When the diameter of atransparent area drops below a certain value, the errors in printingregistration are such that individual transparent areas are reducedsignificantly in diameter.

[0113] The special test image is preferably constructed of all thelayers to be printed and each layer being printed at 100% color. Eachlayer includes the pattern of transparent circles with decreasingdiameter in registration with every other layer. As an example, layersof the colors black, white, magenta, yellow, cyan and black are printedat 100% color intensity sequentially, each layer including the array oftransparent circles. As the colors are at 100%, any missregistrationwill be easily visible as the respective color encroaching into thetransparent areas and reducing their diameters.

[0114] In accordance with the present application, the “localregistration index” (LRI) of the printing method/printer involved, isdefined as the transparent area diameter in mm at which the diameter ofa substantial number of the transparent areas in the printed image hasreduced to 50% of its intended diameter in any direction. Typical valuesare given in Table 1 for some commercial printers. Actual values of LRIdepend on the accuracy of setting up the printer and of calibration. Itis advantageous if the printer in accordance with the present inventionhas a local registration index (LRI) better than (i.e. less than) 1.0 mmand preferably less than 0.6 mm and more preferably about 0.3 mm whenprinting 4 or more colors. TABLE 1 LRI print Printer Type (mm) qualityDPI Encad Novajet Thermal Ink jet 0.6 excellent 360 SummaChrome ™,Thermal transfer ˜0.4* excellent 406 Summagraphics Corp. DesignJet ™HP750C Thermal Ink jet ˜0.4* excellent 360 Hewlet Packard Corp. Xerox8954 Electrostatic 0.7 good 200 multipass 3M Scotchprint ™ 9512Electrostatic, one 0.6 good 400 pass Raster Graphics Inc. Electrostatic,1.0 good 200 DCS 5400 multi-pass

[0115] Generally, the silhouette pattern 2 includes an light restrictinglight colored or white layer or metallic silvery or gold layer whichfaces the display device 3 and/or the display device 4 of FIG. 1. Inaccordance with the present invention, this light restricting lightcolored layer 2 may be printed using light colored, silver metallic orwhite ink or toner depending on the printing method used. A white spotcolor is preferred. “Light restricting” means that the deposited layerhas a transmission optical density (TOD) of at least 1.0, preferably ofat least 2.0, more preferably of 2.5 and most preferably of 3.0 orgreater. The software required for computer graphics using computer 13in accordance with the present invention is modified so that areas ofwhite are printed with the white toner or ink as a spot color, whereasthe transparent areas are “printed” as “no ink” areas.

[0116] To prepare the data for the graphics design, the image 3,4 may befirst created and stored in computer 13 including data for a lightrestricting layer 43. Under-color removal in accordance with theinvention may be carried out on the image data as described above. Theimage is normally stored as color separated layers or planes of data foreach primary printing color. Each of the planes represents the data forone color, e.g. black, cyan, magenta or yellow or a spot color. Withconventional equipinent, data preparation method 7 is used and tilefollowing is created: a 100% black or dark colored plane of datarepresenting layer 42 as the first image 4 within the graphics software.This may be created as a spot color layer. Next, a 100% white, silver orlight colored plane of data representing light colored layer 43 as thelight restricting layer 2 is produced. Finally, the data for layers44-47 as the full color graphics image 3 is generated. The black andwhite layers 42, 43 are preferably specified as spot colors. Thisresults typically in producing 6 sets or planes of data: one for theblack layer 42, one for the white layer 43 and four for layers 44-47 ofmagenta, yellow, cyan and black used for a full-color print. However,the invention is not limited thereto. Where a good quality process blackmay be produced, i.e. a black from a mixture of cyan, magenta andyellow, the final black layer 47 may be omitted. Where a tintedsubstrate is used the first black or dark layer 42 may be omitted. Oneor more of the layers 42-47 may be applied as a plurality of layers. Forinstance, the white layer 43 may be stored as a series of planes of datarepresenting white layer 43 in order to obtain sufficient opacity in thefinal print.

[0117] The array of transparent areas 48 may be generated withincomputer 13 and the image data modified by introducing the transparentareas 48 into each of the layers of data representing the printed layers42-47 by overlaying or other technique. Typically for printing devices16-21, “EPS” Separation files are constructed from the modified imageincluding the transparent areas 48 and these files are communicated tothe relevant intermediate imaging device 16 or printer 20. Alternativelyand preferably, the introduction of the transparent areas 48 into thedata to be printed is delayed to the last possible step before creationof the intermediate imaging substrates 17 or printing to form printedimages 21. This is best achieved using data preparation methods 5,6,8,or 9 in which a separate T layer is output from the computer 13. The Tlayer data is introduced into the CMYK layer data and the silhouettelayer data when the output data from the computer 13 is raster imageprocessed into raster bitmaps of the various print layers 42-47. Thishas the advantage that operating on the data with algorithms, e.g. toprepare print files, change scale, change from Macintosh format to DOSformat, is carried out before small scale repetitive structures such asthe transparent areas 48 are introduced into the image data. Due totruncation errors, small scale repetitive structures in digital data maysuffer distortions when operated on by algorithms. Such distortions mayappear as rhythmic changes of size or shape or loss of part of theimage.

[0118] To protect the printing, a transparent overlaminate 49 may beused which is preferably optically clear. It is preferred if theoverlaminate 49 is the optically clear sheeting in accordance with theeleventh embodiment of the present invention.

[0119] In this application, overlaminate layer 49 refers to any clearmaterial that can be adhered to the surface of any existing coated oruncoated sheet material. “Overlamination” refers to any process ofachieving this adherence, particularly without the entrapment of airbubbles, creases or other defects that might spoil the appearance of thefinished article or image

[0120] The deleterious effects of ambient humidity may be slowed by theoverlamination of a transparent protective coat or sheet herein referredto as an overlaminate. Overlamination has the further advantage that theimages are protected from scratching, splashes, and the overlaminate cansupply a high gloss finish or other desired surface finish or design,and provide a degree of desired optical dot-gain. The overlaminate layer49 may also absorb ultraviolet radiation or protect the underlayers andimage from deleterious effects of direct sunlight or other sources ofradiations. Overlamination is, for example, described in U.S. Pat. No.4,966,804.

[0121] After printing an image or design of the present invention, theimage is preferably overlaminated with a transparent colorless or nearlycolorless material 49. Suitable overlaminate layers 49 include anysuitable transparent plastic material bearing on one surface anadhesive. The adhesive of the overlaminate layer 49 could be a hot-meltor other thermal adhesive or a pressure-sensitive adhesive. The surfaceof the overlaminate layer 49 can provide high gloss or matte or othersurface texture. Preferred overlaminate layers 49 are designed forexternal graphics applications and include materials such as thosecommercially available from 3M Company as Scotchprint™ 8910 ExteriorProtective Film, 8911 Exterior Protective Film, and 8912 ExteriorProtective Film. However, other films are available or could befabricated and the invention is not limited to those exemplified.

[0122] In the absence of the use of a clear, transparent overlaminate, aprotective clear coat of a vinyl/acrylic material may be applied, suchas Product Nos. 3920, 8920, 9720, 66201, and 2120 protective coatingsfrom the Commercial Graphics Division of Minnesota Mining andManufacturing Co. of St. Paul, USA to protect the durable, imagedsubstrate. Such coating may be performed by some printers at the end ofthe image printing process.

[0123] Pressure sensitive adhesives useful for layer 41 can be anyconventional pressure sensitive adhesive that adheres to both layer 41and to the surface of the item upon which the sheeting 40 having thepermanent, accurate image is destined to be placed. Pressure sensitiveadhesives are generally described in Satas, Ed., Handbook of PressureSensitive Adhesives 2nd Ed (Von Nostrand Reinhold 1989), the disclosureof which is incorporated by reference. Pressure sensitive adhesives arecommercially available from a number of sources. Particularly preferredare acrylate pressure sensitive adhesives commercially available fromMinnesota Mining and Manufacturing Company of St. Paul, Minn. andgenerally described in U.S. Pat. Nos. 5,141,790, 4,605,592, 5,045,386,and 5,229,207.

[0124] Non-limiting further examples of pressure sensitive adhesivesuseful with the present invention include those adhesives described inU.S. Pat. Nos. Re. 24,906 (Ulrich); 2,973,826; Re. 33,353;3,389,827;4,112,213; 4,310,509; 4,323,557; 4,732,808; 4,917,929; and5,296,277 (Wilson et al.) and European Publication 0 051 935, thedisclosures of which are incorporated by reference herein. A presentlypreferred adhesive is an acrylate copolymer pressure sensitive adhesiveformed from a 90/10 weight percent monomer ratio of 2-methylbutylacrylate/acrylic acid in a 65/35 heptane/acetone solvent system (39-41%solids) and having an inherent viscosity of about 0.7-0.85 dl/g.

[0125] Thickness of adhesive 318 can range from about 0.012 mm to about1 mm with a thickness of about 0.025 mm (1 mil) being preferred.

[0126] The adhesive may be protected with an optional liner (not shown)which can be constructed from any conventional release liner known tothose skilled in the art for image graphic media Non-limiting examplesinclude Polyslik™ release liners commercially available from RexamRelease of Oak Brook, Ill. and polyester liners such as a 0.096 mmpolyethylene terephthalate film with a matte backside coating on onemajor surface and on the other major surface, a vanadiumoxide/surfactant/sulfopolyester antistatic primer coating and acondensation cure silicone exterior coating. These antistatic coatingsare generally described in U.S. Pat. No. 5,427,835 (Morrison et al.),the disclosure of which is incorporated by reference herein. Ideally theliner is optically flat. The liner preferably has a Sheffield valuebetween 1 and 10.

[0127] Non-limiting examples of further release liners include siliconecoated Kraft paper, silicone coated polyethylene coated paper, siliconecoated or non-coated polymeric materials such as polyethylene orpolypropylene, as well as the polymeric materials coated with polymericrelease agents such as silicone urea, urethanes, and long chain alkylacrylates, such as defined in U.S. Pat. No. 3,957,724; 4,567,073;4,313,988; 3,997,702; 4,614,667; 5,202,190; and 5,290,615; thedisclosures of which are incorporated by reference herein.

[0128] In accordance with the present invention the transparent areas inthe printing may be introduced after the RIP. The printer 20 or theintermediate imaging device 16 may be a “TLD” device configured tointroduce the transparent areas of the image. For instance when printer20 is an inkjet printer, the printer may be configured so that noprinting is carried out for the whole width of a printing substrate atregular intervals. This produces a series of parallel transparent areas.

[0129] Alternatively the printing head may be deactivated a repeatednumber of times to produce a distribution of square or rectangulartransparent areas. If the printer 20 is an electrostatic printer,portions of each printing head may be missing or deactivated, whichproduces a series of longitudinal transparent areas. Portions of theheads may be deactivated in sequence to introduce square or rectangulartransparent areas.

[0130] A TLD printer in accordance with the present invention may becreated by control of the printer 20 using the T layer data. Afterraster image processing, the raster bit maps may be operated on by afurther algorithm using the T layer data which changes the raster bitmap such that transparent areas are produced when printed. Such amodification may be done by a hard-wired circuit in the printer 20 or bysoftware run on a local processor in printer 20. Alternatively, the Tlayer data may be used to control the printing head directly. Forinstance, for an ink jet printer the print signals going to the printinghead may be suppressed in accordance with the T layer data to producetransparent areas at the required positions.

[0131] In accordance with the fourth embodiment of the present inventionthe silhouette pattern 2 and images 3 or 4 are printed using ink-jet orbubble jet printing methods. Ink-jet printing includes a variety ofprocedures including thermal ink-jet printing and piezo-electric ink-jetprinting. All these methods have in common that discrete quantities ofink are sprayed from fine nozzles towards a receptor sheet. Recently,wide format printers have become commercially available, and thereforethe printing of larger articles such as large engineering drawings,blueprints and color posters and signs has become feasible. Suitablereceptor sheeting for non-durable use may be transparent polyestermarking film 8501/8501H, supplied by Minnesota Mining and ManufacturingCompany. The optically clear, flexible vinyl substrate in accordancewith the eleventh embodiment is particularly preferred. The formation ofaccurate inkjet images is provided by a variety of commerciallyavailable printing techniques. A suitable large format printer,including warranted clear films and inks is the Hewlett Packard HPDesign Jet 750C or 755CM printer, supplied by Hewlett PackardCorporation of Palo Alto, Calif., USA, however, may other brands areavailable. Non-limiting examples include thermal inkjet printers such asDeskJet brand, PaintJet brand, Deskwriter brand, DesignJet brand, andother printers commercially available from Hewlett Packard Corporationas well as piezo type inkjet printers such as those from Seiko-Epson,spray jet printers and continuous inkjet printers. To perform theinvention, additional cartridges should be added to the printing head inaddition to the usual four colors, cyan, magenta, yellow and black. Toprint a black layer 42 and a white layer 43 of FIGS. 9 or 10, at leastan additional white station and black station are required. To obtaingood opacity two or more white or black cartridges may be added to theprinting head.

[0132] From the test results shown in Table 1, it can be seen that inkjet printing provides highly accurate local registration printing.Pigmented ink jet printing inks are available from the CommercialGraphics Division of Minnesota Mining and Manufacturing Company (3M).Generally, pigmented ink jet inks from 3M a water-based pigmented inkwhich comprises a suspension of commercially available pigment particlesand a dispersant of a formula of

[0133] wherein R is an alkyl, aryl, or aralkyl group obtained by theremoval of primary amino groups from alkyl, aryl, or aralkyl amines;

[0134] m=1 to 6;

[0135] R³ and R⁴ are hydrogen or lower alkyl;

[0136] R⁵ is the residue of the nitrogen reactive compound selected fromthe group consisting of acylating reagents, carbamoyl halides, sulfamoylhalides, alkylating reagents, alkylating (epoxide) reagents,iso(thio)cyanates, sulfonating reagents, and aziactone reagents;

[0137] wherein R²⁰ and R²¹ are independently, alkyl, aryl, or aralkylgroups, or a cation selected from the group consisting of a proton,lithium, sodium, potassium, ammonium, or tetraalkyl ammonium.

[0138] Pigments for ink jet inks use the standard colors of cyan,magenta, yellow, and black.

[0139] For black inks, carbon black can be used as the black pigment.The selection of carbon blacks suitable for use with the presentinvention is based primarily upon considerations of surface oxidation(high “volatiles” preferred), and the degree of blackness (also calledjetness) of the pigment. Pigments that are acidic or surface-treatedprovide suitable interaction sites for strong dispersant adsorption.Pigments having a high surface oxide content are more hydrophilic, andthereby much easier to disperse. Pigments with a high degree ofblackness or jetness provide a high quality printed image.

[0140] For yellow inks, the use of nickel azo yellow pigment offersseveral advantages. First, such pigments provide inks which are highlydurable in outdoor environments. Second, such pigments contain nickelions which may be able to form complex bonds with the novel dispersants.Lastly, such pigments are believed to offer a high degree of thermalconductivity. As a result, if particle deposition onto a heater elementdoes occur during the jetting process, the deposited film will notsignificantly reduce the heating efficiency of the ink, thereby allowingproper bubble formation. For magenta inks, a primary consideration islightfastness, since it is very desirable to produce graphic images thatare adapted to outdoor applications. Quinacridone magenta pigment isknown to have excellent lightfastness, and therefore, is one preferredmagenta pigment.

[0141] For cyan inks, the considerations above, (i.e., lightfastness,durability, etc.), apply as well. As a variety of satisfactoryproperties may be found using copper phthalocyanine as a cyan pigment,inks comprising such pigments are one preferred embodiment.

[0142] Preferably, pigmented ink jet inks can be prepared withdispersants of the following formula.

[0143] Specific compositions of suitable dispersants are given in theTable below. Ex R* R³ R⁴ R⁵ R⁶ R⁷ R⁸ R⁹ R¹⁰ R¹¹ n a R H H H CH₃ CH₃ C₄H₉Na Na H 2 0 b R H H H CH₃ CH₃ C₈H₁₇ Na Na H 2 0 c R H H H CH₃ CH₃ C₁₂H₂₅Na Na H 2 0 d R H H H CH₃ CH₃ C₁₈H₃₇ Na Na H 2 0 e R H H H CH₃ CH₃CH₂CH₂CH₆CH₅ Na Na H 2 0 f C₆H₅CH₂CH₂ H H H CH₃ CH₃ C₄H₉ Na Na H 3 0 gN(CH₂CH₂)₃ H H H CH₃ CH₃ C₄H₉ Na Na H 3 0 h R H H H CH₃ CH₃ R** C₂H₃C₂H₅ H 2 0 j R H H H CH₃ CH₃ R*** C₂H₅ C₂H₅ H 2 0

[0144] In the practice and the field of the fifth embodiment, the groupswhich are not directly involved in the reaction steps forming thecompounds of the present invention may be substituted to meet desiredphysical property requirements in the final dispersants. This is notonly allowable, but may be highly desirable or essential in theformation of tailored dispersants. Where individual substituents maytolerate such broad substitution; they are referred to as groups. Forexample, the term “alkyl group” may allow for ester linkages or etherlinkages, unsubstituted alkyls, alkyls with such useful substitution ashalogen, cyano, carboxylic ester, sulfonate esters or salts, and thelike. Where the term “alkyl” or “alkyl moiety” is used, that term wouldinclude only unsubstituted alkyls such as methyl, ethyl, propyl, butyl,cyclohexyl, isooctyl, dodecyl, etc.

[0145] In addition to the pigments and dispersants described above, theinks will comprise primarily water as a pigment suspension agent. Suchinks will typically also include further additives to provide variousproperties. For example, an alcoholic polyol, may be employed to controlthe drying rate of the ink. Suitable alcoholic polyols include, forexample, polyalkylene glycols such as polyethylene glycol andpolypropylene glycol, alkylene glycols whose alkylene group has 2-6carbon atoms, such as ethylene glycol, propylene glycol, butyleneglycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexyleneglycol, and diethylene glycol; glycerol; and lower alkyl ethers ofalcoholic polyols such as ethylene glycol monomethyl or monoethyl ether,diethylene glycol methyl or ethyl ether, and triethylene glycolmonomethyl or monoethyl ether. A surfactant, useful for wetting andreducing the surface tension of the ink system, can be provided as well.In addition to the above, other ink additives commonly known in the artmay also be used. These include, water-soluble organic cosolvents,humectants, biocides, fungicides, defoamers, corrosion inhibitors,viscosity modifiers, pH buffers, penetrants, sequestering agents, andthe like. Current compounding technology for the processing of pigmentdispersions employs numerous processing technologies. One suchtechnology makes use of ultrasonic energy to achieve mixing and particledeflocculation.

[0146] Another technology makes use of media mills, such as ball mills,sand mills or attritors. Media mills achieve acceptable pigmentdispersions by subjecting the pigment mixture to high intensitymicroshearing and cascading which breaks down agglomerations of thepigment particles. However, media mill processing systems often sufferfrom disadvantages including media wear product contamination.

[0147] Additionally, if the flow rate in a media mill is raised beyond acertain level, the resulting grinding and dispersion becomes uneven, andmuch of the material leaves the system without being sufficientlyprocessed.

[0148] Problems associated with media milling systems can be overcome,at least in part, using homogenizers and emulsifiers. These systemsgenerally function by forcing a premix of solids and liquids to collideagainst a surface, or to collide against itself. Unfortunately such highpressure devices are considered to be unsuitable for processing pigmentdispersions due to the abrasive nature of the pigment particles and therelatively large size of pigment agglomeration structures which can plugnarrow gaps through which such systems force the mixture being treated.Such clogging can be avoided, at least in part, by filtration orpreprocessing to reduce the size of pigment agglomerations and to ensuresufficient dispersion of the pigment prior to use of high pressureprocessing.

[0149] In still another processing method, the pigment dispersion can beforced through a series of small nozzles having diameters on the orderof about 150 micrometers to about 1000 micrometers. Such systems must beable to withstand very high pressures at high fluid velocities. Threedifferent configurations for such systems may be used: a) a “wedge”configuration with orifices of decreasing diameter, b) a “wedge”configuration within which the orifices have cavitation enhancementdevices, and c) an “impinging jet” configuration in which the dispersionstream is split into at least two elements, each stream is passedthrough an orifice to create a jet, and the jet streams are recombinedby impinging them against each other. Each of these systems has beenfound to yield satisfactory results when processing water-basedpigmented inks.

[0150] After the ink has been processed using either of the “wedge”configurations or the “impinging jet” configuration at a concentrationof about 15 % by weight, it is diluted with an additional amount ofdeionized water and diethylene glycol to produce a final inkconcentration of about 4% concentration with a given diethyleneglycol-to-water ratio. In the dilution step, the dispersion is mixedusing a shear mixer (available, for example, from Silverson MachinesInc., East Longmeadow, Mass.) at moderate speed while water anddiethylene glycol are sequentially added. The addition of diethyleneglycol is carried out slowly to prevent flocculation of the dispersion.

[0151] Following the dilution step, the ink is filtered using, forexample, a 5 micron Whatman Polycap 36 HD cartridge type filter(available from Arbor Technology, Ann Arbor, Mich.). A pump, such as aMasterflex peristaltic pump (available from Barnant Co., Barrington,Ill.) can be used to feed the ink through the filter. A flow rate ofabout 120 milliliters per minute with a back pressure of about 3 psi ispreferred. Further examples of suitable inks are given in the co-pendingUS patent application also owned by Minnesota Mining and ManufacturingCo. having attorney docket number 52146USA4A, Ser. No. 08/556,336 and aPCT application ______ which claims priority therefrom, both of whichare incorporated herein by reference.

[0152] In accordance with the present invention the display device 4 ofFIG. 1 may be a black or dark layer. This layer faces towards the insideof a bus or building window to which the graphic has been applied. It ispreferable that this black layer is uniform and that the graphic isdurable, in particular water resistant.

[0153] Another ink jet formulation replaces the dispersants previouslydescribed with water-soluble silicone polymers such aspoly(dimethylsiloxane)-g-poly(acrylate)s as additives in water-basedpigmented inks for ink jet printing, particularly thermal ink jetprinting. Further information about these ink jet formulations can befound in copending, coassigned PCT patent application serial no. ______incorporated herein by reference.

[0154] Not only the inks but also the ink jet printing substrate ispreferably durable. In accordance with the seventh and eighthembodiments, suitable durable receptor sheetings for durable ink jetprinted graphic products of the present invention will now be described.Advantageously the articles of the seventh and eighth embodiments acceptpigment-based ink jet inks when the substrate is comprised ofweatherable plastic materials, allowing for heat and light stable imageconstructions under such circumstances as are found in exterior signingenvironments.

[0155] Referring to FIG. 11 an ink jet printing sheet (101) of thepresent invention is illustrated comprising (a) an image receiving layer(111-112) on (b) a substrate (110), wherein the sheet may optionallyhave (c) a layer of adhesive (113) coated or laminated to the substrate(110) on the surface away from the image receiving layer (111-112). Theadhesive layer (113) may or may not be backed with release liner (114).In this embodiment (FIG. 11), the image receiving layer (111-112)comprises at least two layers, wherein one layer is a protectivepenetrant layer (112) and one layer is an ink jet receptor layer (111).

[0156] Once the ink jet printing sheet has been imaged with ink jet ink(shown as patches of dried ink containing pigment particles) (115) usingan ink jet printing process, the printed sheet (101) may beoverlaminated with a transparent protective layer (116). The transparentprotective layer (116) may be a transparent plastic sheet bearing on oneside a pressure-sensitive adhesive or hot-melt (thermal) adhesive, or aclear coat, or a processing technique that will affect the surface ofthe printed sheet (101).

[0157] Both ink jet receptor layer (111) and protective penetrant layer(112) have particles (117) and (118), respectively, that contribute tothe performance of the printed sheet.

[0158] Typically, a release liner (114) comprises a paper or plastic orother suitable sheet material coated or otherwise treated with a releasematerial such as a silicone or fluorocarbon type material on at leastone surface in contact with adhesive layer such that adhesive layeradheres to release layer but is easily removed from the release linerwhen desired so that the adhesive layer is exposed.

[0159] Briefly, in one aspect of the seventh embodiment of the presentinvention, an ink jet printing sheet is provided comprising a substrateand an image receiving layer contacting the substrate, wherein the imagereceiving layer comprises of at least one protective penetrant layer ofone composition and at least one ink jet receptor layer of a secondcomposition, and wherein the ink jet receptor layer contains dispersedparticles or particulates of a size that causes protrusions from theprotective penetrant layer. Optionally, on the side of the substrateopposite from the image receiving layer, in sequential order, is anadhesive layer and a release liner.

[0160] An advantage of the seventh embodiment is an ink jet printingsheet wherein the substrate and adhesive are durable for periods ofseveral years in an exterior environment where the materials and imagescan be exposed to rain, sun, and such variations in temperature as arefound in exterior environments and on surfaces in exterior environments.Typically, the articles of the present invention have some flexibilitysuch that it may be adhered onto surfaces having some curvature or nonuniformity e.g. windows with screw heads or rivets, without easilyripping the material or cracking or delamination of the image receivinglayers, overlaminating layers, other coatings or image or “tenting” ofthe material over the protrusion.

[0161] The ink jet printing sheet provides useable images using bothdye-based and pigment-based ink jet inks suitable for use, for example,in wide-format ink jet printers wherein both narrow or wide images canbe made by ink jet printing process The resultant printed sheet iseasily handleable without easy smearing of the image and can be applied,when an adhesive layer is part of the ink jet printing sheet, to awindow, vehicle side or other surface using techniques well known in theart without use of other devices such as spray adhesives.

[0162] Finally, the articles of the seventh embodiment maintain otherdesirable properties of an ideal ink jet printing sheet, such as, dyebleed resistance and low background color. Good color saturation anddensity are also observed in the printed images. The printed articles donot curl excessively on exposure to humidity or during the ink jetprinting process, and printed images exhibit quick ink drying timesfollowing printing with good image sharpness.

[0163] Ink jet printing sheets are commercially available from theCommercial Graphics Division of 3M. Ink jet printing sheets are alsodescribed in PCT Publication WO 96/08377, which is incorporated byreference herein.

[0164] Further embodiments are described in co-pending U.S. patentapplication Ser. No. 08/554,256 and its corresponding PCT patentapplication from claiming priority therefrom, both of which areincorporated herein by reference.

[0165] In accordance with the present invention and shown schematicallyin FIGS. 1, 7 and 8, six or seven layers of ink may be printed withclose registration to each other. It is preferable if the inks are quickdrying. The eighth embodiment of the present invention addresses quickdrying receptor materials for ink jet printers. Further, ink receptorlayers are not perfectly and a method of improving the transparencywould be preferable.

[0166] The eighth embodiment may provide in one aspect an inkjetrecording medium comprising a hydrophilic, microporous, polymericmembrane having opposing major surfaces and a non-porous hygroscopiclayer residing on at least one major surface of the membrane.

[0167] The hygroscopic layer provides a means for receiving an inkjetimage and retaining dyes and pigments contained in the ink.

[0168] The hydrophilic, microporous, polymeric membrane provides a meansfor durably supporting the hygroscopic layer containing the inkjet imageand also a means for diffusing the solvents contained in the inks fromthe dyes and pigments retained in the hygroscopic layer.

[0169] The combination of the hygroscopic layer and the hydrophilic,microporous, polymeric membrane provides the means for rapidly producinga precise inkjet image in a durable medium.

[0170] For purposes of this invention, “hydrophilic” means that thecontact angle of the liquid on the surface is less than 90 degrees. Forpurposes of this invention, “hygroscopic” means the layer is capable ofbeing wet by a water-based blend of solvents and surfactants used ininkjet inks, and the water-based blend is absorbed by the layer. Forpurposes of this invention, “microporous polymeric membrane” means apolymer film that contains an interconnecting void structure. Forpurposes of this invention, “non-porous layer” means a layer that doesnot contain an interconnecting void structure. For purposes of thisinvention, “hydrophilic microporous polymeric membrane” means a polymerfilm whereby the capillary and surface tension forces of the water-basedliquids, such as a blend of solvents and surfactants, will cause theliquid to be absorbed, i.e., to enter the pores of the membrane.Preferably, the membrane will absorb water with less than one atmosphereof pressure. For the purposes of this invention, “precise” means thatdot spread resulting from applying an ink jet drop to the sheet is belowa level at which the resolution of the image is adversely affected.Examples without precise imaging might show image bleed, uneven edges,or mottled colors.

[0171] In an eighth embodiment of the invention, inkjet recording medium210 of FIG. 12 is comprised of a hydrophilic, microporous, polymericmembrane 212 having a hygroscopic layer 214 thereon. The layer 214 canbe coated on or laminated to the membrane 212 using techniques known tothose skilled in the art of coating or laminating of multiple layeredconstructions. Non-limiting examples of coating or laminating techniquesinclude notched bar coating, curtain coating, roll coating, extrusioncoating, gravure coating, calendering, and the like.

[0172] Hydrophilic, microporous, polymeric membrane 212 is hydrophilicand receptive of aqueous solvents typically used in inkjet formulations.Microporous membranes are available with a variety of, pore sizes,compositions, thicknesses, and void volumes. Microporous membranessuitable for this invention preferably have adequate void volume tofully absorb the inkjet ink discharged onto the hydrophilic layer of theinkjet recording medium. It should be noted that this void volume mustbe accessible to the inkjet ink. In other words, a microporous membranewithout channels connecting the voided areas to the hygroscopic surfacecoating and to each other (i.e., a closed cell film) will not providethe advantages of this invention and will instead function similarly toa film having no voids at all.

[0173] Void volume is defined in ASTM D792 as the (1-Bulkdensity/Polymer density)*100. If the density of the polymer is notknown, the void volume can be determined by saturating the membrane witha liquid of known density and comparing the weight of the saturatedmembrane with the weight of the membrane prior to saturation. Typicalvoid volumes for hydrophilic, microporous, polymeric membrane 212 rangefrom 10 to 99 percent, with common ranges being 20 to 90%.

[0174] Void volume combined with membrane thickness determines the inkvolume capacity of the membrane. Membrane thickness also affects theflexibility, durability, and dimensional stability of the membrane.Membrane 212 can have a thickness ranging from about 0.01 mm to about0.6 mm (0.5 mil to about 30 mils) or more for typical uses. Preferably,the thicknesses are from about 0.04 mm to about 0.25 mm (about 2 mils toabout 10 mils).

[0175] The liquid volume of typical inkjet printers is approximately 40to 140 picoliters per drop. Typical resolution is 118 to 283 drops percentimeter. High resolution printers supply smaller dot volumes. Actualresults indicate a deposited volume of 1.95 to 2.23 microliters persquare centimeter with each color. Solid coverage in multicolor systemscould lead to as high as 300% coverage (using undercolor removal) thusleading to volume deposition of 5.85 to 6.69 microliters per squarecentimeter.

[0176] Hydrophilic, microporous, polymeric membrane 212 has a pore sizethat is less than the nominal drop size of the inkjet printer in whichthe inkjet recording medium is to be used. The pore size may be from0.01 to 10 micrometers with a preferred range of from 0.5 to 5micrometers with pores on at least one side of the sheet.

[0177] The porosity, or voided aspect, of membrane 212 need not gothrough the entire thickness of the membrane, but only to a sufficientdepth to create the necessary void volume. Therefore, the membrane maybe asymmetric in nature, such that one side possesses the aforementionedproperties, and the other side may be more or less porous or non-porous.In such a case, the porous side must have adequate void volume to absorbthe liquid in the ink that is passed through the hygroscopic layer 214.

[0178] Non-limiting examples of hydrophilic, microporous, polymericmembranes include polyolefins, polyesters, polyvinyl halides, andacrylics with a micro-voided structure. Preferred among these candidatesare a microporous membrane commercially available as “Teslin” from PPGIndustries as defined in U.S. Pat. No. 4,833,172 and hydrophilicmicroporous membranes typically used for microfiltration, printing orliquid barrier films as described in U.S. Pat. Nos. 4,867,881,4,613,441, 5,238,618, and 5,443,727, which are all incorporated byreference as if rewritten herein. Teslin microporous membrane has anoverall thickness of approximately 0.18 mm, and the void volume has beenmeasured experimentally to be 65.9%. The ink volume capacity of themembrane is thus 11.7 microliters per square centimeter. Therefore, thismembrane has sufficient void volume combined with thickness to fullyabsorb the ink deposited by most inkjet printers, even at 300% coverage,without considering the amount retained in the hygroscopic layer.

[0179] Membrane 212 can optionally also include a variety of additivesknown to those skilled in the art. Non-limiting examples include fillerssuch as silica, talc, calcium carbonate, titanium dioxide, or otherpolymer inclusions. To obtain clarity these fillers may be milled untiltheir particle size is below the wavelength of light. It can furtherinclude modifiers to improve coating characteristics, surface tension,surface finish, and hardness.

[0180] Hygroscopic layer 214 can be a coated layer or laminated layer onthat portion of membrane 212 upon which the inkjet image is to beformed. Thus, layer 214 need not cover completely the membrane 212. Norneed layer 214 cover both sides of membrane 212. Layer 214 preferablylies substantially on the surface of membrane 212 and does not contactthe inner pore surfaces of the membrane. Depending on the ultimatepurpose for the medium 210, at least one side of membrane 212 may becovered at least in part by layer 214 and the other side may be scaledor coated with another material, such as an anti-static coating,adhesive, barrier layer, strength enhancing layer, etc.

[0181] Layer 214 can be constructed from a variety of naturallyoccurring or synthetically constructed materials known to those skilledin the art for providing an ink receptive surface. Non-limiting examplesof the materials used for forming layer 14 include polyvinyl alcohol,polyvinyl pyrrolidone, cellulose derivatives such as carboxymethylcellulose, polyethylene oxide, water soluble starches and gums. Inaddition, inorganic fillers such as silica, talc, calcium carbonate,titanium dioxide can be beneficial to enhance handling, strength,wetting, or control viscosity. Mordants, such as in U.S. Pat. Nos.5,354,813 and 5,403,955 and color stabilizers can also be included.

[0182] Of these materials, hygroscopic, polymeric coatings are preferreddue to ease of manufacturing and performance to provide an ink receptivesurface for receiving and permanently contacting and retaining dyes andpigments in a precise inkjet image. Of these coatings, poly(N-vinyllactams), polyethylene oxides, methyl and propyl cellulose derivatives,and poly(vinyl alcohols) are particularly preferred.

[0183] Hygroscopic layer 214 may be formed on membrane 212 using anumber of techniques, including coating, laminating, or co-extrusion.When a hydrophilic coating solution is applied to the membrane, solutionviscosity and concentration will affect the performance of the resultinginkjet recording medium. For example, low viscosity coating solutionscoated on membranes with very high porosity and/or large pore size tendto fill the pores, resulting in a coated membrane that is saturated withhygroscopic polymer and has little or no coating on the surface.Membranes coated in such a manner do not meet the requirements of thisinvention because the imaged medium usually exhibits lower image densityand contrast and can dry more slowly.

[0184] Preferably, medium 210 after imaging can have the pore structureof membrane 212 collapsed to provide transparency by a post treatmentsuch as heating or calendering, such as disclosed in U.S. Pat. No.5,443,727.

[0185] Further embodiments are given in co-pending U.S. patentapplication Ser. No. 08/614,986 and a PCT patent application claimingpriority therefrom, both of which are incorporated herein by reference.

[0186] Ninth and tenth embodiments of a direct printing method inaccordance with the present invention relate to electrostatic printing.The term “electrostatic” is used for recording processes in which arecording head is utilized to impose an electrostatic pattern upon arecording medium, and in which a toner material is subsequentlyattracted to, and affixed to the electrostatic pattern. Processes ofthis type are employed for preparing engineering graphics, artwork foradvertisements, displays and the like.

[0187] In a typical electrostatic imaging process, a recording headwhich includes a linear array of a plurality of separately chargeableelectrodes, generally referred to as “nibs”, is scanned across arecording medium, and the nibs are selectively energized to impose anelectrostatic pattern upon the medium. The charged medium is contactedwith a toner, which typically comprises a liquid containing a pigment ordye thereon. Excess toner is removed from the medium, leaving toner onlyin the charged areas. The toner is subsequently dried or otherwise fixedto produce a permanent image. The process can be utilized for singlecolor or full color graphics and can be completed in a single passacross the medium or in multiple passes across the medium.

[0188] The recording medium is an important component of theelectrostatic imaging system. The medium must be able to accept, retain,and discharge the electrostatic pattern. The medium must also becompatible with the toner system employed as well as the particularimaging hardware, such as a single or multiple pass electrostaticprinter.

[0189] In accordance with the ninth embodiment of the present inventionelectrostatic printing of media requires the printing of electrostaticimages on a dielectric paper construction followed by transfer of thatimage to polymer films. Such conventional electrostatic imaging isdisclosed in U.S. Pat. No. 5,114,520 (Wang et al.).

[0190] The dielectric paper construction typically comprises a paper orpaper-like substrate, a conductive layer coated on a major surface ofthe substrate, a dielectric layer coated over the conductive layer, anda release layer coated above, beneath, or with the dielectric layer toassure that the image received above the dielectric layer can betransferred to the final substrate upon application of heat andpressure. A commercially available example of this transfer process andthe products to accomplish that process is the Scotchprint™ ElectronicGraphics System available from Minnesota Mining and ManufacturingCompany of St. Paul, Minn. which is one direct printing method inaccordance with the present invention. A further suitable system forcarrying out the present invention is the printer DCS 5400 andassociated inks, including white and silver spot colors for thesilhouette layer 2, available from Raster Graphics Inc., San Jose,Calif., USA.

[0191] Both single pass and multipass electrostatic printers may beused. Multipass printers have a single printing head and feed theappropriate primary color to the head in each pass. In accordance withthe present invention the sequence of toners may be used to print thesequence of colors described with reference to FIGS. 9 and 10: aninitial dark layer 42, a light colored light restricting layer 43 andCMYK layers 44 to 47 or vice versa. Single pass machines have presentlyfour or five printing heads arranged parallel to each other in thelongitudinal printing direction. In accordance with the presentinvention conventional single pass machines may be modified to runmultipass. For instance, a four head electrostatic printer may bemodified to apply the dark layer 42 including printing registrationmarks along the longitudinal edges of the printing substrate, and threeidentical layers of the light restricting layer 43 on top of each otherto increase the opacity of this layer. In the second pass, the CMYKimage layers 44 to 47 are applied using the registration marks tomaintain registration. Alternatively, a five head electrostatic printermay be used to print the dark layer 42, the light restricting layer 43and then CMY image layers 44 to 46 in one pass, using process (CMY)black instead of the final black station. Due to the considerable undercolor removal in accordance with the present invention, a separate black(K, layer 47) is often not necessary.

[0192] A preferred transparent printing substrate, to which the image istransferred from the electrostatic paper, is the optically clear vinylsheeting of the eleventh embodiment. Transfer of the image from theelectrostatic paper to the transparent substrate in the laminator mayresult in some reduction of optical clarity of the printing substrate inthe transparent areas. This can be corrected by running the printedsubstrate through the laminator again after transfer of the image usingan optically flat sheet as a former such as polyester sheet. Polyesterdoes not soften at laminator temperatures so that there is no transferof the image to the polyester. One aspect of the tenth embodiment of thepresent invention is the construction of a film for the direct printingof electrostatic images.

[0193] In one aspect, the direct print film comprises a durable,conformable, polymeric substrate having a conductive layer prepared froma coating solution comprising conductive pigment and organic solvent.Preferably, the conductive pigment in the conductive layer has a bulkpowder resistivity ranging from about 2 to about 15 Ohm-cm.

[0194] “Bulk powder resistivity” means electrical resistivity of thebulk powder used in the conductive pigment according to the followingtest described by E.I.

[0195] DuPont, one of the commercial suppliers of conductive pigments.As described in Capano et al., “The Application of ZELEC ECP in StaticDissipative Systems” (Du Pont Chemicals, Deepwater, N.J. September1992), a cylindrical cell, with electrodes at the top and bottom is usedto make bulk powder resistivity measurements. A weighed amount of powderis placed into the cell and then pressed with a laboratory press into apellet. The resistance between the two electrodes is then measured as afunction of the pressure applied and the thickness of powder pellet. Thebulk powder resistivities of Du Pont conductive pigments commonly rangefrom about 2 Ohm-cm to about 20 Ohm-cm according to this test. Anothersupplier of conductive pigments, Goldschmidt A. G. of Essen, Germany,identifies bulk powder resistivity as “specific resistance” and employsa test method available from Esprit Chemical Company of Rockland, Md.For purposes of this application, the property of “bulk powderresistivity” includes the concept of the property of “specificresistance”.

[0196] In another aspect, the direct print film comprises a durable,conformable, polymeric substrate having on a major surface a conductivelayer coated thereon, and a dielectric layer coated on the conductivelayer, wherein the dielectric layer includes spacer particles andabrasive particles. Spacer particles, which are generally of a lowerhardness than abrasive particles and/or have a more roundedconfiguration than abrasive particles, function to provide a roughnessthat maintains a relatively small gap between the imaging head of theelectrostatic printer and the remaining surface of the direct printfilm. Abrasive particles function to provide abrasivity to contact theimaging head of the electrostatic printer in order to clean oxidationand other unwanted debris from the imaging head.

[0197] Optionally, the direct print film has a field of pressuresensitive adhesive coated on the other major surface of the direct printfilm, protected by a release liner. The field of pressure sensitiveadhesive permits the direct application of the film having an imageprinted thereon to be adhered to a final location.

[0198] An advantage of the present invention is the ability to eliminatemanufacturing steps for the preparation of electrostatic images on afinal substrate.

[0199] An electrostatic direct printing film can have a surfaceresistance in its conductive layer of about 2×10⁵ to about 3×10⁶ Ohms/□and can have a surface resistance in its dielectric layer of greaterthan about 1×10⁸ Ohms/□. This difference in surface resistance resultsin clear, crisp images generated by the electrostatic printer.

[0200] “Surface Resistance” is the measure of D-C resistance ofmoderately conductive materials according to ASTM Test Designations D4496-87 and D 257-93.

[0201] Referring to FIG. 13, a typical construction of a film of thepresent invention 310 comprises a substrate film 312 having on a majorsurface thereof, a conductive layer 314 and a dielectric layer 316. Onthe opposite major surface of film substrate 312 resides optionalpressure sensitive adhesive 318 protected by a release liner 320.

[0202] For electrostatic imaging on film 310, a conductive coating layer314 is provided from an organic solvent-based conductive coatingsolution on the upper major surface of film substrate 312, which can beany substrate described above for prior embodiments. Electronicallyconductive layers employ a plurality of particles of a transparent,electrically conductive material such as antimony doped tin oxide or thelike, disposed in a polymeric matrix. Conductive layer 314 is preparedfrom a solution of a conductive formulation that generally comprises abinder, conductive pigments, dispersant, and organic-based solvent, thelatter of which is removed during the manufacturing process. The weightpercent of solids to organic solvent in the conductive formulation canrange from about 10 to about 40, with about 25 weight percent beingpresently preferred for ease of application to film substrate 312.

[0203] After coating of conductive formulation on film substrate 312 andevaporation or other removal of organic solvent, the thickness orcaliper of the conductive layer 314 can range from about 2 to about 5 μmwith about 3 μm being presently preferred.

[0204] Non-limiting examples of binders include acrylics, polyester, andvinyl binders. Among acrylic binders, carboxylated acrylate binders andhydroxylated acrylate binders are useful for the present invention, suchas those commercially available from Allied Colloids of Suffolk, Va.such as “Surcol SP2” carboxylated acrylate binder and “Surcol SP5hydroxylated acrylate binder. Among some of the polyesters materialswhich can be employed as binders are materials sold by Goodyear ofAkron, Ohio under the brand “Vitel”, of which grades PE222 and PE200 areparticularly suitable for use in the present invention. Also vinylresins such as “UCAR” “VAGD” brand resins from Union Carbide of Danbury,Conn. can also be useful.

[0205] Conductive pigments can include antimony-containing tin oxidepigments or other pigments such as indium doped tin oxide, cadmiumstannate, zinc oxides, and the like.

[0206] Non-limiting examples of antimony-containing tin oxide conductivepigments include those pigments disclosed in U.S. Pat. No. 5,192,613(Work, III et al.), U.S. Pat. No. 4,431,764 (Yoshizumi); U.S. Pat. No.4,965,137 (Ruf); U.S. Pat. No. 5,269,970 (Ruf et al.); and in productliterature for “Tego S” pigments commercially available from GoldschmidtAG of Essen, Federal Republic of Germany and “Zelec” pigmentscommercially available from DuPont of Wilmington, Del. Generallyparticle size should be reduced by a milling process particularly whenthe Goldschmidt Tego S conductive pigment is employed. Pigments arepreferably milled until the particle size is smaller than the wavelengthof visible light. Scattered transmittance of conductive layer 314 shouldbe 10% or lower.

[0207] Particle size of the conductive pigments in the conductive layer314 can range from about 0.02 to about 0.4 μm. Below about 0.02 μmparticle size, the conductive pigment is too easily imbibed with solventaction, whereas at greater than 0.4 μm, the conductive layer 314 mayaffect transparency.

[0208] Preferably, the average particle size can range from about 0.05μm to about 0.2 μm, with particles of about 0.1 μm being most preferred.

[0209] The bulk powder resistivity can range from about 2 to about 15Ohm-cm with about 2 to about 10 Ohm-cm being preferred and about 6 toabout 7 Ohm-cm being presently preferred. With the DuPont pigments, thebulk powder resistivity can be about 2-5 Ohm-cm for “Zelec 3410-T”pigments and 4-15 Ohm-cm for “Zelec 2610-S” found acceptable for thepresent invention. The bulk powder resistivity has been found to beimportant in controlling the final appearance of the image on the directprint film because materials that are too resistive require the use ol alarger amount of conductive pigment can cause an objectionable amount ofbackground color in the final image.

[0210] The “Tego S” particles are identified to have a specificresistance of 10, which is believed to compute to about bulk powderresistivity of about 10.

[0211] A variety of surfactant materials can be employed as dispersantsfor the conductive layer 314 in the present invention, includingnonionic and anionic dispersants In general, anionic dispersants aremost preferred, although the invention is not limited thereto. Oneparticularly preferred anionic dispersant is a material branded“Lactimon” dispersant from BYK-Chemie USA Corporation of Wallingford,Conn. Also commercially available from BYK-Chemie USA Corporation is anonionic dispersant is branded “Anti Terra U” dispersant.

[0212] Non-limiting examples of solvents for the conductive formulationinclude ethyl acetate and ethanol.

[0213] Formulations of the conductive layer 14 require a weight ratiofrom about 5:1 to about 1:1 of pigment:binder with a preference of aweight ratio of 3:1 pigment:binder. When “Tego S” conductive pigment isemployed, the weight ratio can range from about 3.0:1 to about 4.7:1pigment: binder. When the DuPont “Zelec” conductive pigment is employed,the weight ratio can range from about 1:1 to about 4:1 pigment:binder.

[0214] When the pigment to binder ratio falls below 1:1, there isinadequate bulk conductivity of layer 314. When the weight ratio ofpigment:binder exceeds about 5:1, there is insufficient cohesivestrength of the layer 314 on film substrate 312.

[0215] Dielectric layer 316 can be coated on conductive layer 314 toprovide the electrostatic capacitance required for electrostaticimaging.

[0216] The dielectric layer 316 is of relatively high electricalresistivity and contributes to the performance of film 310 for directprinting of images electrostatically. In addition to providing theinterface of film 10 with the recording head and toner, dielectric layer316 covers and protects conductive layer 314 and provides the topsurface for film 310.

[0217] Dielectric layer 316 is coated on layer 314 from a dielectricformulation that comprises particulate matter of both spacer particlesand abrasive particles, preferably in particular ratios dispersed in abinder.

[0218] Both the spacer particles and the abrasive particles should beselected with consideration to the refractive index thereof, so as toprovide index matching to the remainder of dielectric layer 316 and film310. In this manner, film 310 has a uniform transparent appearance. Thespacer particles can be fabricated from a material having sufficientrigidity to withstand coating and handling, but need not be highlyabrasive. Non-limiting examples of materials useful as spacer particlesinclude relatively soft materials such as a polymer or a mineral orrelatively hard materials such as silica or glass, provided that suchrelatively hard materials have a relatively rounded configuration. Moreparticularly, useful spacer particles can be made from syntheticsilicas, glass micro beads, natural minerals, polymeric materials suchas polypropylene, polycarbonate, fluorocarbons or the like.

[0219] Typically spacer particles have an average size ranging fromabout 1 to about 15 μm, and preferably below about 10 μm. In general,spacer particles will be present in a distribution of sizes, although itis most preferred that the particles remain in a size range of about3-10 μm. To improve transparency particle sizes may be reduced to 0.4 μmor below.

[0220] One particularly preferred group of spacer particle materialscomprise amorphous silica, of which is most preferred the synthetic,amorphous silicas sold by the W. R. Grace Corporation under the brand“Syloid 74”. These materials have an average particle size ofapproximately 3.5-7.5 μm as measured on a Coulter apparatus and anaverage particle size of 6-10 μm as measured on a Malvern analyzer. Onespecific member of this group of materials comprises “Syloid 74X-Regular” particles which have an average particle size of 6.0 asmeasured on a Coulter apparatus.

[0221] Abrasive particles useful for dielectric layer 316 of the presentinvention are provided to assure that the performance of spacerparticles and abrasive are effectively decoupled so as to provide anoptimized dielectric medium.

[0222] The abrasive particles will generally be harder than the spacerparticle material chosen and will usually have a more irregularconfiguration or texture than the spacer particle material. Among someof the preferred abrasive materials are silica materials such asmicrocrystalline silica and other mined or processed silicas, as well asother abrasives such as carbides and the like.

[0223] The abrasive particles generally have the same size range as thespacer particles, typically in the range of about 1 to about 15 μm andpreferably less than 10 μm.

[0224] One particularly preferred group of abrasive materials comprisesmined, microcrystalline silica sold under the brand “Imsil” by UniminSpecialty Minerals, Inc. of Elko, Ill. These materials comprise 98.9%silica with minor amounts of metal oxides. One grade having particularutility comprises “Imsil A-10” which has a median particle size of 2.2μm, and range of particle sizes such that 99% of the particles have asize less than 10 μm and 76% of the particles have a size of less than 5μm

[0225] The proportion of spacer particles to abrasive particles are suchthat the spacer particles are present in a larger amount. Preferably,the ratios of spacer to abrasive particles fall within the range ofabout 1.5:1 to about 5.1. Most preferably, the ratio of spacer toabrasive particles is approximately 3:1.

[0226] The spacer particles and abrasive particles are disposed is abinder which generally comprises a polymeric resin. The resin should beof fairly high electrical resistivity, and should be compatible withboth types of particles and the toner. The resin should have sufficientdurability and flexibility to permit it to function in the electrostaticimaging process and should be stable in ambient atmospheric conditionsand transparent.

[0227] There are large number of resins that meet these criteria. Onepreferred group of materials are the acrylic copolymers of the typecommercially available from Rohm and Haas of Philadelphia, Pa. under thebrand “Desograph-E342-R”.

[0228] A coating mixture to prepare dielectric layer 316 can employsolvents such toluene into which the binder, spacer particles, andabrasive particles can be added as solids. The range of total solids inthe coating mixture can be from 10 to about 35 and preferably about 15to 25 weight percent of the total coating mixture. Of the total solids,the binder solids can comprise from about 93 to about 78 and preferably82 weight percent. Of the total solids, the particles solids (preferablyin a 3:1 spacer:abrasive mixture) can comprise from about 7 to about 22and preferably 18 weight percent.

[0229] The particle solids for the coating mixture can be blended byball milling for approximately two hours at room temperature. Underthese conditions, there is no significant reduction in particlemorphology, and the ball milling process only serves to mix and dispersethe particles. Other processes could be employed.

[0230] There is a conflict between the need for surface roughness forgood printing and a need for a smooth surface to provide goodtransparency. Surface roughness is desired to provide topography fordeposition of toner particles is based on a Sheffield measurement methoddescribed in TAPPI Test T 538 om-88 published by the TechnicalAssociation of the Pulp and Paper Industry of Atlanta, Ga., incorporatedherein by reference. For printing, the dielectric layer 316 should havea surface roughness ranging from about 50 to about 200 Sheffield unitsand preferably from about 80 to about 180 with 140 being presentlypreferred. On the other hand, a surface with less than 10 Sheffieldunits is preferred for transparent, particularly optically clear areasin the print. According to the present invention it is preferred toprint onto a surface of 50 to 80 Sheffield units (lower end of theacceptable range) and then to subject the finished print to a post-printcallendering process using an optically flat former such as an opticallyclear polyester film.

[0231] Referring again to FIG. 13, a pair of electroconductive groundstripes 322 and 324 can be provided in order to aid in the prevention of“leading edge fog” by providing an avenue for residual charge to beeliminated from the ground plane. These stripes 322 and 324 ranging fromabout 0.76 to about 2.54 mm wide are applied to dielectric layer 316 atopposing lateral edges of film 310.

[0232] Stripes 322 and 324 can be made from a conductive ink sold underthe brand “Multifilm, Conductive Black Ink 9093E20J” from Raffli andSwanson of Wilmington, Mass. and are configured to permeate dielectriclayer 316 at such lateral edges of film in order to provide anelectrical ground to the conductive layer 312.

[0233] Thus, a film 310 of the present invention can have in sequentialorder, a release liner 320 comprising from about 0.07 to about 0.15 mm(about 3 to about 6 mils) thickness, a field of pressure sensitiveadhesive 318 comprising about 0.03 mm (about 1 mil) thickness, a filmsubstrate 312 comprising from about 0.05 to about 0.10 mm (about 2 toabout 4 mils) thickness, a conductive coating layer 314 comprising fromabout 1 to about 5 micrometers (0.04-0.2 mils), a dielectric layer 316comprising from about 2 to about 4 micrometers (0.08-0.16 mils)thickness, and a pair of electroconductive ground stripes 322 and 324 atlateral edges of film 310 that permeate layer 316 to layer 314.

[0234] A preferred method of constructing films of the present inventioncomprises a modular construction, but can comprise a sequentialconstruction. In the sequential construction, beginning with releaseliner 320, each of the layers 318, 316, 314 and 312 are built on top ofrelease liner 320.

[0235] Preferably, the method of the present invention employs a modularconstruction wherein the first step is the casting of a film organosolonto a temporary release liner, preferably an optically flat releaseliner in accordance with the eleventh embodiment of the presentinvention, followed by fusing the organosol to form a substrate 312according to techniques known to those skilled in the art. In anindependent module, the field of pressure sensitive adhesive 318 is caston release liner 320, preferably an optically flat liner in accordancewith the eleventh embodiment of the present invention and the techniquesdescribed later. Then, the module of film substrate 312 on the temporaryliner is joined with the module of field of pressure sensitive adhesive318 on liner 318 and the temporary liner is discarded.

[0236] Alternatively, one can employ a commercially available pressuresensitive adhesive-backed polymeric film in substitution for the abovedescribed modular construction.

[0237] Conductive layer 314 can be coated on film substrate 312 usingany technique known to those skilled in the art, preferably a wire barcoating technique as known to those skilled in the art. The # wire barof from about 6 to about 40 is used to achieve the 1-5 micrometerthickness described as suitable for layer 314, with a #10 wire bar beinguseful for DuPont conductive particles and a #12 to #40 wire bar beinguseful for Tego conductive particles. The wire bar coating process stepcan operate at a line speed ranging from about 9 meters per minute toabout 19 meters per minute and preferably about 12 meters per minute (40feet per minute).

[0238] Dielectric layer 316 is coated on conductive layer 14 accordingto coating techniques known to those skilled in the art, preferably areverse gravure coating of the dielectric layer 316 onto conductivelayer 314. In those instances where a wire bar is utilized, the totalsolids are preferably about 16 weight percent. Where a reverse gravureprocess is employed, the total solids are preferably about 25 weightpercent. The ruling mill cylinder having a theoretical “lay down” factorof about 0.031 mm to about 0.078 mm is used to achieve the 1.5-5micrometer thickness described as suitable for layer 316 with 3micrometer thickness being preferred. The reverse gravure coatingprocess step can operate at a line speed ranging from about 1.5 to about62 meters per minute, and preferably about 15 meters per minute. Thereverse gravure can operate at a roll ratio ranging from about 0.5 toabout 1.5, and preferably about 1.0.

[0239] When ground stripes 322 and 324 are employed, such stripes can beapplied to lateral edges of film 310 using techniques known to thoseskilled in the art, preferably an offset gravure or flexographic coatingof stripes 322 and 324. Stripes 322 and 324 permeate layer 316 at suchlateral edges to create a ground path from stripes 322 and 324 to layer314. The offset gravure or flexographic coating process step can operateat a line speed ranging from about 12 meter per minute to about 31meters per minute, and preferably about 15 meters per minute (50 feetper minute).

[0240] After imaging, film 310 can be protected with overlaminate filmsas has been described previously. The overlaminating film of theeleventh embodiment of the present invention is particularly preferred.

[0241] Films 310 of the present invention can provide an average colordensity as measured according to a “Reflective Optical Density of aStatus T Method” under the requirements of ANSI/ISO 5/3-1984, ANSI PH2.18-1985 published by the Graphic Communications Association ofArlington, Va. of from about 1.0 to about 1.6 O.D. Units. Preferably,the average color density ranges from about 1.3 to about 1.5 O.D. Units.These values show that films 310 of the present invention has anexcellent color imaging capability after electrostatic printing directlyonto film 310 using electrostatic printers otherwise used for theprocesses described in Wang et al. and Chou et al. above.

[0242] Before calendering, films 310 of the present invention canprovide a 60° Gloss from about 10 to about 30. 60° Gloss can be measuredas described in ASTM D2457-90 (1990). After post-print calendering,transparent areas of film 310 may have a 60° Gloss of 100 to 150.Further embodiments are given in co-pending U.S. patent application Ser.No. 08/581,324 which is incorporated herein by reference.

[0243] Sheeting for overlaminates and printable substrates for use inthe embodiments in accordance with the present invention are preferablyflexible, weather resistant and optically clear. A suitable substrate isa vinyl sheeting in accordance with an eleventh embodiment of thepresent invention. Optionally the sheeting may be provided with anoptically clear adhesive.

[0244] While the optically clear, transparent overlaminates and printingsubstrates known in the art and mentioned above are quite acceptable forlarge format graphics uses, vinyl-based optically clear, transparentoverlaminate and printing substrate films remain extremely elusive toachieve.

[0245] One aspect of the eleventh embodiment of the present invention isan inexpensive, durable, optically clear, transparent layer formed on apolymeric release liner that has preferred surface properties to permitthe layer of the present invention to have optical clarity withinacceptable ranges.

[0246] This layer in accordance with the eleventh embodiment of theinvention comprises a composition comprising vinyl chloride resin,optional acrylic resin, optional plasticizer, and optional stabilizer,wherein the composition is formed on a polymeric release liner havingthickness values from about 0.05 mm (0.002 inches) to about 0.12 mm(0.005 inches).

[0247] The method of forming the layer comprises the steps of: formingthe optically clear, transparent layer having two major surfaces from anorganosol on a first polymeric release liner having a thickness rangingfrom about 0.05 mm (0.002 inches) to about 0.127 mm (0.005 inches);optionally adhering a field of pressure sensitive adhesive to a secondrelease liner; and optionally laminating the field of pressure sensitiveadhesive to an exposed major surface of the optically clear, transparentlayer; and optionally removing the first polymeric release liner.

[0248] An advantage of the eleventh embodiment is the ability of thedurable, optically clear, transparent layer to provide stabilization andprotection from abrasion and ultraviolet light degradation. As shown inFIG. 9, the printing layers 42 to 47 on printing substrate 41 may beprotected by an overlaminate 49 which may be the overlaminate inaccordance with the eleventh embodiment. However, the vinyl layer inaccordance with the eleventh embodiment may also be the printingsubstrate and overlaminate 41 of FIG. 10 which is adhered to a substratesuch as a glass window by adhesive 50 with the image 42-47 therebetween.Therefore, the present invention not only includes printing on to thevinyl layer in accordance with the eleventh embodiment but also includesa method of protecting an image in accordance with the presentinvention, comprising the steps of forming a layer of the eleventhembodiment on a polymeric release liner; and laminating the layer of theeleventh embodiment over the image.

[0249]FIG. 14 shows a preparation composite 410 comprising a durable,optically clear, transparent layer 412 of a thermally processableorganosol composition on a polymeric release liner 414 having smoothsurface properties helpful in the formation of the optical clarityproperties of layer 412.

[0250] Liner 414 can be made-from a polymeric release liner materialknown to those skilled in the art that has a surface roughness, measuredaccording to Haggerty Sheffield (see above), of from about 1 to about 10Sheffield units. Selection of the liner 414 should recognize the natureof the surface of liner 414 contacting layer 412 will determine theappearance of the outer surface of layer 412 on the durable, imagedsubstrate. Non-limiting examples of release liners include siliconecoated polyester, urea alkyd coated polyester, and the like.Particularly preferred for release liner 414 is a urea alkyd coatedpolyester having a urea polymer coating comprising a polyurea alkydformulation of 0.005 mm caliper on a 0.07 mm polyester film.

[0251] Release liner 414 can have a gloss ranging from about 100 toabout 150 and preferably from about 120 to about 140. Gloss is measuredby a Gardner 60° Glossmeter using published techniques known to thoseskilled in the art such as ASTM Standard No. D523.

[0252] Durable, optically clear, transparent layer 412 comprises athermally processable composition containing vinyl chloride, optionaladditional thermally processable resins, an optional plasticizer, and anoptional stabilizer where the layer can be prepared from an organosolwith a sufficient melt temperature to be thermally processable to causelayer 412 to form on the polymeric release liner 414 without causingharm to the surface of liner 414 responsible for formation of theoptical clarity properties of the layer 412.

[0253] Vinyl chloride is an industrial chemical commercially availablefrom many sources throughout the world. Preferably, the vinyl chlorideuseful in the present invention is a vinyl chloride resin comprisingGeon vinyl chloride resin commercially available from B. F. GoodrichChemical Company of Cleveland, Ohio.

[0254] When used as another, but optional resin, in the formation oflayer 12, acrylic resin is readily available as an industrial chemicalcommercially available from many sources throughout the world.Desirably, the acrylic resin useful in layer 12 comprises from about75,000 to about 125,000 number average molecular weight. Preferably, theacrylic resin useful in the present invention is an acrylic resincomprising Elavacite acrylic resin having about 100,000 molecular weightcommercially available from ICI Resins of Wilmington, Del.

[0255] Optionally, the composition for layer 412 comprises a plasticizerto aid in the formation of layer 12 and its transfer to a durable,imaged substrate. Non-limiting examples of plasticizer include1,4-butylene glycol; adipic acid; butyloctyl phthalate; hydrocarbonresins; di(2-ethylhexyl) azelate; dibutyl azelate; dihexyl azelate; andthe like. Particularly preferred for a plasticizer, if present in thecomposition of layer 12, is Vikoflex 7170 plasticizer commerciallyavailable from ATOChem of Philadelphia, Pa.

[0256] Optionally, the composition for layer 412 comprises a stabilizerto aid in the formation of layer 412, provide ultraviolet resistance,and assist transfer to a durable, imaged substrate. Non-limitingexamples of stabilizer include Hal-Lub, Hal-Base, Hal-Carb, Hal-Stabbrand hindered amine light stabilizers commercially available fromHal-stab Company of Hammond, Ind.; Nuostabe V1923 brand ultravioletlight stabilizer commercially available from Witco of Greenwich, Conn.;Cosorb brand ultraviolet light stabilizer commercially available from 3MCompany of St. Paul, Minn.; and Tinuvin brand HAL stabilizerscommercially available from Ciba-Geigy Corp. of Greensboro, N.C.Particularly preferred for a stabilizer, if present in the compositionof layer 12, is Tinuvin 1130 and Tinuvin 292 HAL stabilizers fromCiba-Geigy or Nuostabe V1923 stabilizer.

[0257] The layer 412 can have a composition ranging from about 40 toabout 60 weight percent of vinyl chloride, from about 10 to about 30weight percent acrylic resin, from about 0 to about 33 weight percentplasticizer, and from about 0 to about 10 weight percent stabilizer.

[0258] Desirably, layer 412 can have composition ranging from about 45to about 55 weight percent of vinyl chloride, from about 15 to about 30weight percent acrylic resin, from about 0 to about 20 weight percentplasticizer, and from about 0 to about 8 weight percent stabilizer.

[0259] Preferably, layer 412 can have composition ranging from about 47to about 60 weight percent of vinyl chloride, from about 16 to about 27weight percent acrylic resin, from about 10 to about 21 weight percentplasticizer, and from about 2 to about 6 weight percent stabilizer.

[0260] Composition for layer 412 can be prepared by dissolving theingredients into solvents such as ketones and aromatics, preferablyDi-isobutyl ketone, mineral spirits, methyl ethyl ketone, methylisobutyl ketone and toluene, more preferably in equal parts of suchsolvents. Layer 412 is knife or gravure coated on liner 414 with a drycoating weight ranging from about 0.70 to about 1.10 g to yield a drythickness of from about 0.04 ml (0.0015 inches) to about 0.08 mm.,(0.0030 inches). Preferably, liner 414 has a thickness ranging fromabout 0.5 mm (0.002 inches) to about 1 mm and layer 412 has a thicknessranging from about 0.5 mm (0.002 inches) to about 1 mm.

[0261] After coating, layer 412 is dried on liner 414 to remove solventsat a temperature ranging from about 90° C. to about 120° C. for about 2minutes, then it is fused in an oven for 30 seconds to 60 seconds at175° C. to 205° C. Composite 410 is then stored until usage, optionally,but preferably as a portion of a lamination with a field of pressuresensitive adhesive (PSA) and a second release liner protecting the PSAfield.

[0262]FIG. 15 illustrates a laminated composite 420, formed from thelamination of a PSA field 416 (protected by second release liner 418)laminated to a major surface of layer 412 opposite polymeric releaseliner 414.

[0263] Field 416 and liner 418 are combined in a separate step prior tolamination according to techniques well known to those skilled in theart.

[0264] Field 416 can be any conventional pressure sensitive adhesivethat has optical clarity at least as good as and preferably better thanthe optical clarity properties of layer 412. Non-limiting examples ofsuch adhesives include polyacrylates, polyvinyletliers, natural rubber,silicone, rubber, styrene butadiene, cis-polybutadiene, styrene-isopreneblock copolymers. Preferably, adhesives used include vinyl acrylicblends having a weight percent ratio ranging from about 50/50 to about90/10 and preferably about 75/25 and a viscosity of 1100-1500centipoise.

[0265] Field 416 can have a laminated thickness of from about 0.013 mmto about 0.05 mm, and preferably from about 0.015 to about 0.03 mm.

[0266] Release liner 418 can be made from a release liner material knownto those skilled in the art. Preferably, the release liner material 418has a surface roughness, measured according to Haggerty Sheffield offrom about 5 to about 40 Sheffields. Selection of the liner 418 willaffect the appearance of layer 412 and PSA field 16 during storage andprior to usage, which may be material to customer preference for thelayer of the present invention. Non-limiting examples of release linersinclude silicone coated polyester, silicone coated paper, urea alkydcoated polyester, urea alkyd coated paper, and the like. Particularlypreferred for release liner 418 is a silicone coated polyestercommercially available from Rexani Release of Oak Brook, Ill. having asilicone coating of 0.005 mm caliper on a 0 07 mm polyester film.

[0267] Release liner 418 can have a gloss ranging from about 80 to about130 and preferably from about 100 to about 130. Gloss is measured by aGardner 60° Glossmeter using published techniques known to those skilledin the art such as ASTM Standard No. D523.

[0268] After lamination of PSA field 416 to layer 412, first polymericrelease liner 414 can be removed prior to storage and use.

[0269]FIG. 16 illustrates the cross-sectional appearance of finalcomposite 430 composed of layer 412 having PSA field 416 adhered to amajor surface thereof and also adhered to a substrate 422 having animage 424 on the major surface thereof to which field 416 is adhered.Layer 412 and PSA field 416 contact a major surface of substrate 422without enveloping substrate 422. Preferably, substrate 422 has image424 on one major surface and a field 424 of adhesive (not shown) on theopposing major surface. Image 424 is formed in accordance with thepresent invention.

[0270] Image 424 can comprise dyes, pigments, or combinations of bothfrom toners, inks, or paints, all as known to those skilled in the art,in particular those described in embodiments of the present invention.

[0271] Preferably, image 424 comprises compositions capable ofwithstanding processing temperatures of at least about 100° C., andpreferably at least about 105° C. This film surface is receptive to mostinks, pigments, toners, dyes, and paints.

[0272] Substrate 422 can be any transparent substrate known to thoseskilled in the art of image graphics. Non-limiting examples includetransparent glass, transparent acrylic sheets and transparentpolycarbonate sheets. Substrate 422 may be the window of a building orvehicle.

[0273] Layer 412 and PSA field 416 are transferred from liner 418 oncomposite 420 to image 424 and substrate 422 by application of pressureof a range sufficient to adhere PSA field 416 to substrate 422 andpreferably from about 1 kg. to about 5 kg.

[0274] Layer 412 and PSA field 416 can have a combined caliper of fromabout 0.05 mm (0.002 inches) to about 0.13 mm when adhered to image 424and substrate 422. Preferably, the caliper ranges from about 0.10 mm toabout 0.13 mm

[0275] After layer 412 and PSA field 416 are applied to image 424 andsubstrate 422, liner 18 can be removed, rolled, and can be recycled forlater use.

[0276] Machinery conventionally used in the formation of durable imagedsubstrates can be used for the pressure sensitive transfer of layer 412to substrate 422. Non-limiting examples of machinery include laminatorssuch as Scotchprint™ 9540 and 9542 brand laminators from 3M Company.

[0277]FIG. 17 illustrates a twelfth embodiment of the present inventionwhere an image 426 is placed on layer 412 of composite 410 prior toadhering of PSA field 416. Transfer layer 412 and PSA field 416, withimage 426 between layer 412 and PSA field 416, is adhered to a substrate422 (with or without a second image 424 as seen in FIG. 17) to becomefinal composite 430. In this embodiment, an electrostatic imagingtransfer process can be used such as the Scotchprint™ Electronic Imagingsystem and electrostatic imaging paper, such as No. 8601 image transferpaper, both commercially available from Minnesota Mining andManufacturing Co. St. Paul, USA, to place a 4-color design andsilhouette pattern layer toner image from the electrostatic paper ontolayer 412. Optionally, a PSA field 416 is adhered and the liner 414 ispealed away leaving image 426 on layer 412 for lamination transfer to adesirable durable film. Alternatively, any of the printing methods ofthe embodiments of the present invention, e.g. ink-jet or thermaltransfer, may be used to print the image onto layer 412. Thermal masstransfer printing in accordance with the thirteenth embodiment isparticularly preferred.

[0278] Use of layer 412 provides abrasion and ultraviolet lightprotection to image 424, image 426, or both, and substrate 422.

[0279] Abrasivity for layer 412 of the present invention before theimage 424 wears away ranges from about 500 to about 2000 cycles withCS-10 abrasion wheels commercially available from Taber Industries ofTonowanda, N.Y. and preferably from about 500 to about 1000 cycles,depending the type of substrate used

[0280] Layer 412 provides protection to image 424 and substrate 422without detracting from the appearance of the image. Layer 418 isoptically clear, transparent as determined by visual perception.Preferably, optical clarity gives acceptable vision when measured with astandard vision test with and without the film between one's eyes andthe vision chart.

[0281] A protective clear layer was prepared on an urea alkyd coatedpolyester having a urea polymer coating comprising a polyurea alkydformulation of 0.005 mm caliper on a 0.07 mm polyester film from thefollowing components.

[0282] 46.7 weight percent Geon 178 vinyl resin (B. F. Goodrich,Cleveland, Ohio); 17.9 weight percent Elvacite acrylic resin (ICIResins, Wilmington, Del.), 17.2 weight percent Vikoflex 7170 plasticizer(ATOChem, Philadelphia, Pa.); 2.3 weight percent Tinuvin 292 HALstabilizer (Ciba-Geigy, Greensboro, N.C.), 2.3 weight percent NuostabeV1923 stabilizer (Witco, Greenwich, Conn.) and 13 6 weight percent of asolvent system of two parts of di-isobutyl ketone and one part mineralspirits.

[0283] A layer was knife coated on the liner with a wet thickness of0.127 mm and dried to remove solvents at a temperature of 120° C. for 2minutes, and then fused in an oven for 45 seconds at 175° C. to a drythickness of about 0.05 mm.

[0284] An adhesive was prepared from the following components: VYHH(Union Carbide, Danbury, CT) 69 parts Acryloid B82 (Rohm and Haas,Philadelphia, PA) 17 parts Paraplex G62 (C. P. Hall, Bedford Park, IL)14 parts

[0285] The components were dissolved in a solvent mixture comprised ofequal parts xylol, methyl ethyl ketone and methyl isobutyl ketone toyield a final solution viscosity of 1100-1600 centipoise. A field ofsolution was knife coated at 0.076 mm wet thickness on a silicone coatedpolyester release liner having a silicone coating of 0.005 mm caliper ona 0.07 mm polyester film (Rexam Release, Chicago, Ill.) and dried at120° C. for 2 minutes to obtain a dry thickness of 0.0025 mm.

[0286] The layer on liner from Example 9 was then contacted to theadhesive field from Example 10 to produce the laminate as seen in FIG.15, applying a pressure of about 2.3 Kg/cm².

[0287] In accordance with a thirteenth and particularly preferredembodiment of the present invention, the display device 20,21 of thepresent invention is a thermal transfer, including thermal mass transferor sublimation printer. In thermal mass transfer printing a donor sheetor “ribbon” is placed in contact with a receptor sheet and the donorsheet is heated in an imagewise manner (usually from the back) by alocalized thermal print head. The imagewise distribution of heat (andpressure, if necessary) causes an imagewise transfer of material fromthe donor sheet to the receptor sheet. The material transferred isusually a binder containing colorant (e.g. a dye, pigment or mixture ofthe two). The binder is a thermally softenable material (e.g. a wax or aresin), which releases from a carrier layer on the donor sheet andtransfers and adheres to the receptor sheet. The thermal head typicallyconsists of a matrix of minute heating elements, each of which can beaddressed individually, normally with highly controlled pulses ofcurrent being passed through resistors which comprise the heatingelements. Recently, large format thermal mass transfer printers havebecome commercially available with good local registration, e.g. theSummaChrome™ Imaging system (406 DPI) from Summagraphics Corporation,USA., or the GerberScientific Products/Gerber Edge Graphtec Corp. USA/GC1300 system (400 DPI), or Roland Digital Group ColorCamm PNC-5000 system(360 DPI). Such systems can be addressed directly by the computer 13 ofthe present invention.

[0288] Thermal sublimation printers differ from thermal mass transferprinters in that the donor ribbon does not contact the receptor sheet.The term “sublimation” refers to the fact that the colorant layer on thedonor ribbon vaporizes and condenses onto the receptor sheet withoutgoing through an intermediate liquid state. By controlling the number ofcurrent pulses sent to each cell of the thermal printing head, the heatgenerated can be controlled which, in turn, determines the amount ofsublimation and hence, the color density at that location. An example ofa sublimation printer is the Rainbow™ series of printers supplied byMinnesota Mining and manufacturing Co., St. Paul, USA. These printersare typically small format.

[0289] Ribbons and printing methods for thermal transfer printing oflight restricting including opaque silver metallic, white opaque andbrilliant durable colors are known, for example, from U.S. Pat. No.5,409,883 and U.S. Pat. No. 5,312,683 as well as U.S. Pat. No. 5,472,932which are all incorporated herein by reference. The light restrictingwhite and silver metallic ribbons known from U.S. Pat. No. 5,409,883 andU.S. Pat. No. 5,312,683 are preferred to print the light restrictinglight colored silhouette pattern 2 in registry with the colored image3,4 of the present invention onto a suitable substrate. The opticaldensity of the white light restricting layer should be at least 1,preferably at least 2, more preferably at least 2 5 and most preferably3.

[0290] Extremely smooth, optically clear substrates having a very flatsurface are preferred as the transfer process is sensitive to surfaceerrors and the final sheeting should restrict vision as little aspossible. The clear vinyl sheeting in accordance with the eleventhembodiment of the present invention is particularly preferred. Thermaltransfer colorants used in thermal transfer ribbons are advantageous ascommercially available ribbons provide UV light and moisture resistantimages in full color.

[0291] For example, the SummaChrome™ Imaging system (406 DPI) fromSummagraphics Corporation, USA includes a printer with eight stationsfor up to eight different ribbons each of which can be conveyed to thethermal printing head individually and in any order. Four of theseribbons may be the conventional black, magenta, yellow and cyan ribbonswith four other ribbons being spot colors, in particular at least anlight restricting light colored ribbon, such as metallic silver or whiteribbons as mentioned above. Resin based ribbons are preferred as theyprovide good scratch resistant prints with good weatherability anddurability. Trials with the SummaChrome™ Imaging system havedemonstrated very good local registration between multiple layers ofdifferent colored ribbons (see Table 1) resulting in exact registrationprinting down to transparent area diameters of less than 1 mm.

[0292] The substrate for thermal transfer printing may be commerciallyavailable, clear, particularly optically clear films such as thetransparent marking film VM 4414 from Minnesota Mining and ManufacturingCo., St. Paul, USA or commercially available optically clear polyesterfilms. Particularly preferred are the optically clear vinyl films inaccordance with the eleventh embodiment of the present invention. Inorder to give adequate mechanical stability to the vinyl film, it ispreferably supplied in a laminate form with a polyester film withoptional pressure sensitive adhesive between the vinyl and thepolyester.

[0293] In accordance with the fourteenth to sixteenth embodiments of thepresent invention the TLD device 14 in accordance with the presentinvention may be a combination of direct printers 60, 70 or acombination of direct printer types in a printer 80.

[0294] The fourteenth to sixteenth embodiments of the present inventionprovide printed substrates of exceptional quality providing transparentareas 6 with optical clarity and free of printing aids and also coloredimages of the highest quality.

[0295] As shown schematically in FIG. 18, the output of computer 13which includes both CMYK image data as well as T-layer data is suppliedto printer 60 and optionally also to printer 70. Printer 60 is used toprint a special silhouette pattern 2 onto a conformable, translucent ortransparent, preferably optically clear substrate. The vinyl substrateof the eleventh embodiment is particularly preferred. The output print62 from printer 60 is fed to printer 70 which may be a separate printeror a printing head integrated with the printing head of printer 60. Thefinal full color image 3 including transparent areas 6 is produced byprinter 80 as a final print 72.

[0296] Referring to FIGS. 19A and 19B, the transparent substrate 63,which may be any of the translucent, transparent and/or optically clearsubstrates mentioned in the previous embodiments, particularly theoptically clear, conformable substrate of the eleventh embodiment, isprinted with layers 64 to 66 in registry leaving transparent areas 67 inaccordance with the transparency data from the T layer. Printer 60 ispreferably a thermal transfer printer as described with reference to thethirteenth embodiment. Layer 64 is a dark colored layer equivalent tolayer 42 of FIG. 9 or 10. Layer 65 is a light colored silhouette layerand preferably has a transmission optical density of at least 1,preferably at least 2, more preferably at least 2,5 and most preferablyat least 3. The white and metallic ribbons described in U.S. Pat. Nos.5,312,683 and 5,409,883 are preferred. Layer 66 is a colorant receptorlayer printed at the same time as layer 65 or printed as a separatelayer.

[0297] Certain general principles about colorant receptor layers aredescribed in U.S. Pat. No. 5,472,932. In accordance with the presentinvention, layer 66 may be an ink jet image receptor layer, for instanceas described with reference to the seventh embodiment of the presentinvention including both a penetrant layer and an ink receiving layer.Alternatively, layer 66 may be the hygoscopic layer of the eighthembodiment and the substrate 63 may be the microporous layer of the sameembodiment. Alternatively, layer 66 may be the conductive and dielectriclayers of the tenth embodiment. Conductivity is maintained by providinga continuous path in layer 66 about the transparent areas 67 as bestshown in FIG. 19B. The ribbons for printer 60 may be produced byembedding the particular type of colorant receptor layer in a suitableresin or wax.

[0298] As the colorant receptor layer 66 is placed in registry with thelight colored layer 65, there is no need for layer 66 to be transparent.This has the advantage that receptor layer 66 may be better optimizedfor acceptance of the inks or toners. In particular the particle sizelimitations required in the ninth embodiment may be relaxed. For theconductive layer, the particle range may be extended to 0.02 to 10 μm.Also the surface roughness may be increased to 200 Sheffield unitswithout affecting the clarity of the transparent areas 67.

[0299] The pigments, particles and other materials required for thecolorant receptor layer 66 may be incorporated into a suitable binderfor transferring to layer 65 by heat and pressure as is known forthermal transfer printing.

[0300] Printed substrate 62 may be transferred to a second printer 70.When printer 70 is an electrostatic printer, the substrate 62 may beprinted directly in the printer 70 as described in the tenth embodimentof the present invention. Surprisingly, the transparent areas 67, whichcontain no dielectric and conductive layer, do not receive charge and donot take up toner. Hence, there is no need to provide printer 70 withthe T layer data. This method of printing should be distinguished overEuropean Patent No. EP 0234121 and U.S. Pat. No. B1 4,925,705 in which amask is used and subsequently removed. In accordance with thisembodiment no mask is used.

[0301] The fifteenth embodiment of the present invention will bedescribed with reference to FIG. 20. Substrate 62 is prepared asdescribed above whereby layer 66 is an ink jet ink receptor layer. Thesubstrate 62 is printed in a modified ink jet printer 70. As shown inFIG. 20 the printer 70 may include a conventional four color ink jetprinting head 76 which runs on a guide 71 across the width of thesubstrate 62. Associated with head 76 is a continuous tape havingclosely spaced registration marks. A sensor (not shown) in head 76detects the marks on tape 77 and sends reference position data of thehead 76 to the printer control circuit (not shown). Attached to the head76 is a light source 78 which may be a laser and which provides a narrowbeam of light directed substantially perpendicular to the substrate 62.On the other side of substrate 62 is mounted a head 74 on a furtherguide 73. head 74 is driven synchronously with head 76 by means ofsynchronized stepper motors or DC servomotors as is known in the art.Alternatively a mirror may be placed in the position of guide 73 andboth head 74 and light source 78 may be mounted on the head 76. Head 74includes a light sensor 75. When the light beam from light source 78passes through transparent region 67 of substrate 62, the sensor 75sends a signal 79 to the control circuit of the printer. The controlcircuit modifies the print signal 69 to head 76 so that printing is onlycarried out in registry with layers 63 to 66.

[0302] A sixteenth embodiment of the present invention will be describedwith reference to FIG. 21. Items with the same reference numbers areidentical to those of the fourteenth and fifteenth embodiments. Theprinter 80 includes a thermal transfer printer 84, 86 to 89 and an inkjet printer 85, 90 to 93 combined in a single head. Thermal transferprinter 84,86 to 89 includes two or more ribbons, 88,89 which printlayers 64 to 66 onto substrate 62. The ribbons are held in ribboncarriers 86,87. The thermal printer prints layers 64 to 66 on top ofeach other and in the width of one pass of the ink jet printer 85. Undercontrol of the printer control circuit, the ink jet printer 85 thenprints a full color image in registry with the patterned layers 64 to 66using CMYK cartridges 90 to 93. The combined printing head may bemounted on a guide 81 supported by supports 82, 83 at each end and maytraverse the width of substrate 62 as is conventional for ink jetprinters. A registration mark tape such as 77 of FIG. 20 may be used toimprove registry as is conventional in ink jet printers. Alternatively,the printing head may be stationary and the substrate 62 is moved in theX-Y directions by means of a known X-Y plotter drive.

[0303] As the ink jet printer does not print in areas where there are nolayers 64 to 66, these areas do not require ink receptor layers. Thetransparent areas 67 may therefore be maintained optically clear.

[0304] While some embodiments of the invention have been described, theinvention is not limited thereto. For example, various ways ofidentifying the invention include the following.

[0305] A method of displaying an image on a display device having firstand second sides, said image including an light restricting silhouettepattern having a plurality of first transparent or translucent areas,and at least one design layer having at least one color, said at leastone design layer being visible from one side of said display device andsubstantially less visible from the other side, said image beingsubstantially transparent or translucent as viewed from the other side,comprises the steps:

[0306] 1) providing at least a definition of said design layer to acomputer;

[0307] 2) generating a computerized version of said design layer withthe computer,

[0308] 3) outputting the computerized version of said design layer tosaid display device, the computerized version of said design layer beingmodified to subdivide said design layer into a plurality of seconddiscrete transparent or translucent areas and other areas, and

[0309] 4) displaying said modified design layer and said silhouettepattern with said first and second transparent areas being in registry.

[0310] The method also can have a display device be an LCD display. Themethod can have the first step include providing a definition of asilhouette layer to the computer, the second include generating acomputerized version of said silhouette layer, and the third stepincludes outputting the computerized versions of said silhouette layerand said design layer, the computerized version of said silhouette layerbeing modified to subdivide said silhouette layer into the plurality ofsaid first discrete transparent or translucent areas. The method canhave third step include introducing the plurality of said seconddiscrete transparent or translucent areas into said computerized versionof said design layer using the computer. The method can have the thirdstep include introducing the plurality of said first discretetransparent or translucent areas into said computerized version of saidsilhouette layer using the computer. The method can have said displaydevice be a printer. The method can have the printer be a direct orindirect printer. The method can have the printer be a local exactregistry printer. The method can have the local registry index of theprinter be smaller than 1 mm, preferably smaller than 0.6 mm and mostpreferably smaller than 0.4 mm. The method can have said computerizedversion of said design layer include data of color-separated layers ofsaid design layer. The method can have said computerized versions ofsaid design layer and said silhouette layer include data of said firsttransparent or translucent areas as separate transparency data. Themethod can have said display device be a transparent layer displaydevice.

[0311] An article can have a conformable substrate and comprise: acolorant receptor layer and a light restricting layer on said substrate,said light restricting layer having a plurality of first transparent ortranslucent areas.

[0312] The article can have a conformable substrate, further comprising:said colorant layer having a plurality of second transparent ortranslucent areas, and said first transparent or translucent areas beingin registry with second transparent or translucent areas. The articlecan have colorant receptor layer include a conductive layer suitable forelectrostatic printing. The article can have said receptor layer includea dielectric layer suitable for electrostatic printing. The article canhave said conductive layer include a conductive pigment comprisingparticles of antimony intimately mixed with tin oxide. The article canhave the particles be antimony doped tin oxide. The article can havesaid conductive layer have a surface resistance ranging between 2.0×10⁵to about 3×1O ⁶ Ohms/□. The article can have the dielectric layercomprise spacer particles and abrasive particles with the ratio ofspacer particles to abrasive particles present within the range of about1.5:1 to about 5:1. The article can have colorant receptor layer includea conductive layer suitable for electrostatic printing. The article canhave said receptor layer include a dielectric layer suitable forelectrostatic printing. The article can have said substrate be avinyl-containing polymeric substrate. The article can have said colorantreceptor layer include an ink receiving layer suitable for ink jetprinting The article can have said colorant receptor layer include anink receiving layer suitable for ink jet printing. The article can havesaid substrate include a hydrophilic, microporous, polymeric membraneand said colorant receptor layer includes a hygroscopic layer. Thearticle can have the pore structure of the membrane be collapsed toprovide transparency by a post treatment after imaging such as heatingor calendering. The article can further comprise a protective penetrantlayer and said ink receiving layer containing dispersed particles of asize that causes protrusions from the protective layer. The article cancomprise a protective penetrant layer and said ink receiving layercontaining dispersed particles of a size that causes protrusions fromthe protective layer. The article can be durable. The article can havesaid substrate be transparent, preferably optically clear.

[0313] An article can comprise a polymeric substrate having acomposition comprising vinyl chloride resin, optional acrylic resin,optional plasticizer, and optional stabilizer, wherein the compositionis formed on a polymeric release liner having smoothness of a Sheffieldvalue of from about 1 to about 10, and a light restricting layer and adesign layer on said substrate, said design layer including at least onecolor layer, said light restricting layer being subdivided into aplurality of first transparent or translucent areas, said design layerbeing subdivided into a plurality of second transparent or translucentareas, and said first and second transparent areas being in registry.

[0314] The article can further comprise acrylic resin. The article canhave the amount of vinyl chloride resin range from about 49 to about 72weight percent; the amount of acrylic resin ranges from about 9 to about33 weight percent; the amount of plasticizer ranges from about 0 toabout 25 weight percent; and wherein the stabilizer ranges from about 0to about 8 weight percent. The article can have the amount of vinylchloride resin range from about 55 to about 65 weight percent; theamount of acrylic resin ranges from about 16 to about 27 weight percent;and the composition includes an amount of plasticizer ranging from about10 to about 16 weight percent; and an amount of stabilizer the rangingfrom about 2 to about 6 weight percent. The article can have saidsubstrate be transparent, preferably optically clear.

[0315] A printer for receiving a print file includes color separatedimage data, light restricting layer data and transparency data, and forprinting the color separated image and the light restricting layer dataincluding transparent areas in both the color-separated layer and thelight restricting layer in accordance with the transparency data.

[0316] The printer can be an electrostatic printer, an ink jet printer,or a thermal transfer printer. The electrostatic printer can include alinear array of a plurality of separately chargeable electrodes, andsaid printer prints said transparency data by selectively controllingones of the separately chargeable electrodes. The ink jet printerincludes a plurality of ink jet heads and said printer prints saidtransparency data by selectively controlling ones of said ink jet heads.The thermal mass transfer printer can print said light restricting layerand a further printer device to print said color separated image data.

[0317] A raster image processing method for raster image processing of aprint file including color separated image data, light restricting layerdata and transparency data, can comprise operating on said print file togenerate raster image bitmaps for said color separated image data andsaid light restricting layer data, and introducing said transparencydata into said raster image bitmaps for said color separated image dataand said light restricting layer data so that the transparent areas insaid color separated image raster bitmap and said light restrictinglayer bitmap are in registry.

[0318] The raster image processing method can have said color separatedimage raster bitmap and said light restricting layer bitmap are firstcreated and then said transparent areas are introduced.

[0319] A raster image processing system for raster image processing of aprint file including color separated image data, light restricting layerdata and transparency data, comprises means operating on said print fileto generate raster image bitmaps for said color separated image data andsaid light restricting layer data, and means introducing saidtransparency data into said raster image bitmaps for said colorseparated image data and said light restricting layer data so that thetransparent areas in said color separated image raster bitmap and saidlight restricting layer bitmap are in registry.

[0320] The raster processing system can be hard-wired. The rasterprocessing system can include a programmable digital processor.

[0321] A graphics computer based system for creating graphics imagesincluding color separated layers and light restricting layers, comprisesfirst input means for image data, means for generating color separatedimage data from said image data, means for generating light restrictinglayer data, second input means for transparency data, and means foroutputting a display file including said color separated image data,said light restricting layer data and said transparency data.

[0322] The graphics computer based system can further comprise storagemeans for storing a plurality of standard transparency data templates.

[0323] The claims follow.

What is claimed is:
 1. A method of printing comprising the steps ofcontrolling the ratio of transmission optical density to reflectiveoptical density at any area of an image graphic by use of computersoftware and printing the image onto a substrate.
 2. An imaged graphichaving at least one area where the ratio of transmission optical densityto reflective optical density has been controlled by by use of computersoftware during printing of the image onto a substrate.
 3. A method ofdisplaying an image on a display device having first and second sides,said image including an light restricting silhouette pattern having aplurality of first transparent or translucent areas, and at least onedesign layer having at least one color, said at least one design layerbeing visible from one side of said display device and substantiallyless visible from the other side, said image being substantiallytransparent or translucent as viewed from the other side, comprising thesteps: 1) providing at least a definition of said design layer to acomputer; 2) generating a computerized version of said design layer withthe computer, 3) outputting the computerized version of said designlayer to said display device, the computerized version of said designlayer being modified to subdivide said design layer into a plurality ofsecond discrete transparent or translucent areas and other areas, and 4)displaying said modified design layer and said silhouette pattern withsaid first and second transparent areas being in registry.
 4. An articlecan have a conformable substrate and comprise: a colorant receptor layerand a light restricting layer on said substrate, said light restrictinglayer having a plurality of first transparent or translucent areas. 5.An article having a conformable substrate and comprising: a colorantreceptor layer and a light restricting layer on said substrate, saidlight restricting layer having a plurality of first transparent ortranslucent areas.
 6. An article comprising a polymeric substrate and alight restricting layer and a design layer on said substrate, saiddesign layer including at least one color layer, said light restrictinglayer being subdivided into a plurality of first transparent ortranslucent areas, said design layer being subdivided into a pluralityof second transparent or translucent areas, and said first and secondtransparent areas being in registry.
 7. A printer for receiving a printfile includes color separated image data, light restricting layer dataand transparency data, and for printing the color separated image andthe light restricting layer data including transparent areas in both thecolor-separated layer and the light restricting layer in accordance withthe transparency data.
 8. A raster image processing method for rasterimage processing of a print file including color separated image data,light restricting layer data and transparency data, comprising operatingon said print file to generate raster image bitmaps for said colorseparated image data and said light restricting layer data, andintroducing said transparency data into said raster image bitmaps forsaid color separated image data and said light restricting layer data sothat the transparent areas in said color separated image raster bitmapand said light restricting layer bitmap are in registry.
 9. A graphicscomputer based system for creating graphics images including colorseparated layers and light restricting layers, comprises first inputmeans for image data, means for generating color separated image datafrom said image data, means for generating light restricting layer data,second input means for transparency data, and means for outputting adisplay file including said color separated image data, said lightrestricting layer data and said transparency data.